Provided by: pg-auto-failover-cli_2.1-2_amd64 
NAME
pg_auto_failover - pg_auto_failover Documentation
The pg_auto_failover project is an Open Source Software project. The development happens at
https://github.com/citusdata/pg_auto_failover and is public: everyone is welcome to participate by
opening issues or pull requests, giving feedback, etc.
Remember that the first steps are to actually play with the pg_autoctl command, then read the entire
available documentation (after all, I took the time to write it), and then to address the community in a
kind and polite way — the same way you would expect people to use when addressing you.
NOTE:
The development of pg_auto_failover has been driven by Citus Data, since then a team at Microsoft. The
Citus Data team at Microsoft generously maintains the pg_auto_failover Open Source Software so that
its users may continue using it in production.
For enhancements, improvements, and new features, consider contributing to the project. Pull Requests
are reviewed as part of the offered maintenance.
NOTE:
Assistance is provided as usual with Open Source projects, on a voluntary basis. If you need help to
cook a patch, enhance the documentation, or even to use the software, you're welcome to ask questions
and expect some level of free guidance.
INTRODUCTION TO PG_AUTO_FAILOVER
pg_auto_failover is an extension for PostgreSQL that monitors and manages failover for postgres clusters.
It is optimised for simplicity and correctness.
Single Standby Architecture
[image: pg_auto_failover Architecture with a primary and a standby node] [image] pg_auto_failover
architecture with a primary and a standby node.UNINDENT
pg_auto_failover implements Business Continuity for your PostgreSQL services. pg_auto_failover
implements a single PostgreSQL service using multiple nodes with automated failover, and automates
PostgreSQL maintenance operations in a way that guarantees availability of the service to its users and
applications.
To that end, pg_auto_failover uses three nodes (machines, servers) per PostgreSQL service:
• a PostgreSQL primary node,
• a PostgreSQL secondary node, using Synchronous Hot Standby,
• a pg_auto_failover Monitor node that acts both as a witness and an orchestrator.
The pg_auto_failover Monitor implements a state machine and relies on in-core PostgreSQL facilities to
deliver HA. For example. when the secondary node is detected to be unavailable, or when its lag is
reported above a defined threshold (the default is 1 WAL files, or 16MB, see the
pgautofailover.promote_wal_log_threshold GUC on the pg_auto_failover monitor), then the Monitor removes
it from the synchronous_standby_names setting on the primary node. Until the secondary is back to being
monitored healthy, failover and switchover operations are not allowed, preventing data loss.
Multiple Standby Architecture
[image: pg_auto_failover Architecture for a standalone PostgreSQL service] [image] pg_auto_failover
architecture with a primary and two standby nodes.UNINDENT
In the pictured architecture, pg_auto_failover implements Business Continuity and data availability by
implementing a single PostgreSQL service using multiple with automated failover and data redundancy.
Even after losing any Postgres node in a production system, this architecture maintains two copies of
the data on two different nodes.
When using more than one standby, different architectures can be achieved with pg_auto_failover,
depending on the objectives and trade-offs needed for your production setup.
Multiple Standbys Architecture with 3 standby nodes, one async
[image: pg_auto_failover architecture with a primary and three standby nodes] [image] pg_auto_failover
architecture with a primary and three standby nodes.UNINDENT
When setting the three parameters above, it's possible to design very different Postgres architectures
for your production needs.
In this case, the system is setup with two standby nodes participating in the replication quorum,
allowing for number_sync_standbys = 1. The system always maintains a minimum of two copies of the data
set: one on the primary, another one on either node B or node C. Whenever we lose one of those nodes,
we can hold to this guarantee of two copies of the data set.
Adding to that, we have the standby server D which has been set up to not participate in the
replication quorum. Node D will not be found in the synchronous_standby_names list of nodes. Also, node
D is set up in a way to never be a candidate for failover, with candidate-priority = 0.
This architecture would fit a situation where nodes A, B, and C are deployed in the same data center or
availability zone, and node D in another. Those three nodes are set up to support the main production
traffic and implement high availability of both the Postgres service and the data set.
Node D might be set up for Business Continuity in case the first data center is lost, or maybe for
reporting the need for deployment on another application domain.
Citus Architecture
[image: pg_auto_failover architecture with a Citus formation] [image] pg_auto_failover architecture
with a Citus formation.UNINDENT
pg_auto_failover implements Business Continuity for your Citus services. pg_auto_failover implements a
single Citus formation service using multiple Citus nodes with automated failover, and automates
PostgreSQL maintenance operations in a way that guarantees availability of the service to its users and
applications.
In that case, pg_auto_failover knows how to orchestrate a Citus coordinator failover and a Citus worker
failover. A Citus worker failover can be achieved with a very minimal downtime to the application,
where during a short time window SQL writes may error out.
In this figure we see a single standby node for each Citus node, coordinator and workers. It is
possible to implement more standby nodes, and even read-only nodes for load balancing, see Citus
Secondaries and read-replica.
QUICK START
pg_auto_failover includes the command line tool pg_autoctl that implements many commands to manage your
Postgres nodes. To implement the Postgres architectures described in this documentation, and more, it is
generally possible to use only some of the many pg_autoctl commands.
This section of the documentation is a short introduction to the main commands that are useful when
getting started with pg_auto_failover. More commands are available and help deal with a variety of
situations, see the Manual Pages for the whole list.
To understand which replication settings to use in your case, see Architecture Basics section and then
the Multi-node Architectures section.
To follow a step by step guide that you can reproduce on your own Azure subscription and create a
production Postgres setup from VMs, see the Azure VMs Tutorial section. To get started with a local setup
using docker-compose to run multiple Postgres nodes, see the Tutorial section.
To understand how to setup pg_auto_failover in a way that is compliant with your internal security guide
lines, read the Security settings for pg_auto_failover section.
Command line environment, configuration files, etc
As a command line tool pg_autoctl depends on some environment variables. Mostly, the tool re-uses the
Postgres environment variables that you might already know.
To manage a Postgres node pg_auto_failover needs to know its data directory location on-disk. For that,
some users will find it easier to export the PGDATA variable in their environment. The alternative
consists of always using the --pgdata option that is available to all the pg_autoctl commands.
Creating Postgres Nodes
To get started with the simplest Postgres failover setup, 3 nodes are needed: the pg_auto_failover
monitor, and 2 Postgres nodes that will get assigned roles by the monitor. One Postgres node will be
assigned the primary role, the other one will get assigned the secondary role.
To create the monitor use the command:
$ pg_autoctl create monitor
The create the Postgres nodes use the following command on each node you want to create:
$ pg_autoctl create postgres
While those create commands initialize your nodes, now you have to actually run the Postgres service that
are expected to be running. For that you can manually run the following command on every node:
$ pg_autoctl run
It is also possible (and recommended) to integrate the pg_auto_failover service in your usual service
management facility. When using systemd the following commands can be used to produce the unit file
configuration required:
$ pg_autoctl show systemd
INFO HINT: to complete a systemd integration, run the following commands:
INFO pg_autoctl -q show systemd --pgdata "/tmp/pgaf/m" | sudo tee /etc/systemd/system/pgautofailover.service
INFO sudo systemctl daemon-reload
INFO sudo systemctl enable pgautofailover
INFO sudo systemctl start pgautofailover
[Unit]
...
While it is expected that for a production deployment each node actually is a separate machine (virtual
or physical, or even a container), it is also possible to run several Postgres nodes all on the same
machine for testing or development purposes.
TIP:
When running several pg_autoctl nodes on the same machine for testing or contributing to
pg_auto_failover, each Postgres instance needs to run on its own port, and with its own data
directory. It can make things easier to then set the environment variables PGDATA and PGPORT in each
terminal, shell, or tab where each instance is started.
Inspecting nodes
Once your Postgres nodes have been created, and once each pg_autoctl service is running, it is possible
to inspect the current state of the formation with the following command:
$ pg_autoctl show state
The pg_autoctl show state commands outputs the current state of the system only once. Sometimes it would
be nice to have an auto-updated display such as provided by common tools such as watch(1) or top(1) and
the like. For that, the following commands are available (see also pg_autoctl watch):
$ pg_autoctl watch
$ pg_autoctl show state --watch
To analyze what's been happening to get to the current state, it is possible to review the past events
generated by the pg_auto_failover monitor with the following command:
$ pg_autoctl show events
HINT:
The pg_autoctl show commands can be run from any node in your system. Those command need to connect
to the monitor and print the current state or the current known list of events as per the monitor view
of the system.
Use pg_autoctl show state --local to have a view of the local state of a given node without connecting
to the monitor Postgres instance.
The option --json is available in most pg_autoctl commands and switches the output format from a human
readable table form to a program friendly JSON pretty-printed output.
Inspecting and Editing Replication Settings
When creating a node it is possible to use the --candidate-priority and the --replication-quorum options
to set the replication properties as required by your choice of Postgres architecture.
To review the current replication settings of a formation, use one of the two following commands, which
are convenient aliases (the same command with two ways to invoke it):
$ pg_autoctl show settings
$ pg_autoctl get formation settings
It is also possible to edit those replication settings at any time while your nodes are in production:
you can change your mind or adjust to new elements without having to re-deploy everything. Just use the
following commands to adjust the replication settings on the fly:
$ pg_autoctl set formation number-sync-standbys
$ pg_autoctl set node replication-quorum
$ pg_autoctl set node candidate-priority
IMPORTANT:
The pg_autoctl get and pg_autoctl set commands always connect to the monitor Postgres instance.
The pg_autoctl set command then changes the replication settings on the node registration on the
monitor. Then the monitor assigns the APPLY_SETTINGS state to the current primary node in the system
for it to apply the new replication settings to its Postgres streaming replication setup.
As a result, the pg_autoctl set commands requires a stable state in the system to be allowed to
proceed. Namely, the current primary node in the system must have both its Current State and its
Assigned State set to primary, as per the pg_autoctl show state output.
Implementing Maintenance Operations
When a Postgres node must be taken offline for a maintenance operation, such as e.g. a kernel security
upgrade or a minor Postgres update, it is best to make it so that the pg_auto_failover monitor knows
about it.
• For one thing, a node that is known to be in maintenance does not participate in failovers. If you
are running with two Postgres nodes, then failover operations are entirely prevented while the
standby node is in maintenance.
• Moreover, depending on your replication settings, enabling maintenance on your standby ensures that
the primary node switches to async replication before Postgres is shut down on the secondary,
avoiding write queries to be blocked.
To implement maintenance operations, use the following commands:
$ pg_autoctl enable maintenance
$ pg_autoctl disable maintenance
The main pg_autoctl run service that is expected to be running in the background should continue to run
during the whole maintenance operation. When a node is in the maintenance state, the pg_autoctl service
is not controlling the Postgres service anymore.
Note that it is possible to enable maintenance on a primary Postgres node, and that operation then
requires a failover to happen first. It is possible to have pg_auto_failover orchestrate that for you
when using the command:
$ pg_autoctl enable maintenance --allow-failover
IMPORTANT:
The pg_autoctl enable and pg_autoctl disable commands requires a stable state in the system to be
allowed to proceed. Namely, the current primary node in the system must have both its Current State
and its Assigned State set to primary, as per the pg_autoctl show state output.
Manual failover, switchover, and promotions
In the cases when a failover is needed without having an actual node failure, the pg_auto_failover
monitor can be used to orchestrate the operation. Use one of the following commands, which are synonyms
in the pg_auto_failover design:
$ pg_autoctl perform failover
$ pg_autoctl perform switchover
Finally, it is also possible to “elect” a new primary node in your formation with the command:
$ pg_autoctl perform promotion
IMPORTANT:
The pg_autoctl perform commands requires a stable state in the system to be allowed to proceed.
Namely, the current primary node in the system must have both its Current State and its Assigned State
set to primary, as per the pg_autoctl show state output.
What's next?
This section of the documentation is meant to help users get started by focusing on the main commands of
the pg_autoctl tool. Each command has many options that can have very small impact, or pretty big impact
in terms of security or architecture. Read the rest of the manual to understand how to best use the many
pg_autoctl options to implement your specific Postgres production architecture.
TUTORIAL
In this guide we’ll create a Postgres setup with two nodes, a primary and a standby. Then we'll add a
second standby node. We’ll simulate failure in the Postgres nodes and see how the system continues to
function.
This tutorial uses docker-compose in order to separate the architecture design from some of the
implementation details. This allows reasoning at the architecture level within this tutorial, and better
see which software component needs to be deployed and run on which node.
The setup provided in this tutorial is good for replaying at home in the lab. It is not intended to be
production ready though. In particular, no attention have been spent on volume management. After all,
this is a tutorial: the goal is to walk through the first steps of using pg_auto_failover to implement
Postgres automated failover.
Pre-requisites
When using docker-compose we describe a list of services, each service may run on one or more nodes, and
each service just runs a single isolated process in a container.
Within the context of a tutorial, or even a development environment, this matches very well to
provisioning separate physical machines on-prem, or Virtual Machines either on-prem on in a Cloud
service.
The docker image used in this tutorial is named pg_auto_failover:tutorial. It can be built locally when
using the attached Dockerfile found within the GitHub repository for pg_auto_failover.
To build the image, either use the provided Makefile and run make build, or run the docker build command
directly:
$ git clone https://github.com/citusdata/pg_auto_failover
$ cd pg_auto_failover/docs/tutorial
$ docker-compose build
Postgres failover with two nodes
Using docker-compose makes it easy enough to create an architecture that looks like the following
diagram:
[image: pg_auto_failover Architecture with a primary and a standby node] [image] pg_auto_failover
architecture with a primary and a standby node.UNINDENT
Such an architecture provides failover capabilities, though it does not provide with High Availability
of both the Postgres service and the data. See the Multi-node Architectures chapter of our docs to
understand more about this.
To create a cluster we use the following docker-compose definition:
version: "3.9" # optional since v1.27.0
x-node: &node
build:
context: ../..
dockerfile: Dockerfile
tags:
- pg_auto_failover:tutorial
volumes:
- /var/lib/postgres
environment:
PGDATA: /var/lib/postgres/pgaf
PGUSER: tutorial
PGDATABASE: tutorial
PG_AUTOCTL_HBA_LAN: true
PG_AUTOCTL_AUTH_METHOD: "trust"
PG_AUTOCTL_SSL_SELF_SIGNED: true
PG_AUTOCTL_MONITOR: "postgresql://autoctl_node@monitor/pg_auto_failover"
expose:
- 5432
services:
app:
build:
context: .
dockerfile: Dockerfile.app
environment:
PGUSER: tutorial
PGDATABASE: tutorial
PGHOST: node1,node2
PGPORT: 5432
PGAPPNAME: tutorial
PGSSLMODE: require
PGTARGETSESSIONATTRS: read-write
monitor:
image: pg_auto_failover:tutorial
volumes:
- /var/lib/postgres
environment:
PGDATA: /var/lib/postgres/pgaf
PG_AUTOCTL_SSL_SELF_SIGNED: true
expose:
- 5432
command: |
pg_autoctl create monitor --auth trust --run
node1:
<<: *node
hostname: node1
command: |
pg_autoctl create postgres --name node1 --run
node2:
<<: *node
hostname: node2
command: |
pg_autoctl create postgres --name node2 --run
node3:
<<: *node
hostname: node3
command: |
pg_autoctl create postgres --name node3 --run
To run the full Citus cluster with HA from this definition, we can use the following command:
$ docker-compose up app monitor node1 node2
The command above starts the services up. The first service is the monitor and is created with the
command pg_autoctl create monitor. The options for this command are exposed in the environment, and could
have been specified on the command line too:
$ pg_autoctl create postgres --ssl-self-signed --auth trust --pg-hba-lan --run
While the Postgres nodes are being provisionned by docker-compose, you can run the following command and
have a dynamic dashboard to follow what's happening. The following command is like top for
pg_auto_failover:
$ docker-compose exec monitor pg_autoctl watch
After a little while, you can run the pg_autoctl show state command and see a stable result:
$ docker-compose exec monitor pg_autoctl show state
Name | Node | Host:Port | TLI: LSN | Connection | Reported State | Assigned State
------+-------+------------+----------------+--------------+---------------------+--------------------
node2 | 1 | node2:5432 | 1: 0/3000148 | read-write | primary | primary
node1 | 2 | node1:5432 | 1: 0/3000148 | read-only | secondary | secondary
We can review the available Postgres URIs with the pg_autoctl show uri command:
$ docker-compose exec monitor pg_autoctl show uri
Type | Name | Connection String
-------------+---------+-------------------------------
monitor | monitor | postgres://autoctl_node@58053a02af03:5432/pg_auto_failover?sslmode=require
formation | default | postgres://node2:5432,node1:5432/tutorial?target_session_attrs=read-write&sslmode=require
Add application data
Let's create a database schema with a single table, and some data in there.
$ docker-compose exec app psql
-- in psql
CREATE TABLE companies
(
id bigserial PRIMARY KEY,
name text NOT NULL,
image_url text,
created_at timestamp without time zone NOT NULL,
updated_at timestamp without time zone NOT NULL
);
Next download and ingest some sample data, still from within our psql session:
\copy companies from program 'curl -o- https://examples.citusdata.com/mt_ref_arch/companies.csv' with csv
( COPY 75 )
Our first failover
When using pg_auto_failover, it is possible (and easy) to trigger a failover without having to
orchestrate an incident, or power down the current primary.
$ docker-compose exec monitor pg_autoctl perform switchover
14:57:16 992 INFO Waiting 60 secs for a notification with state "primary" in formation "default" and group 0
14:57:16 992 INFO Listening monitor notifications about state changes in formation "default" and group 0
14:57:16 992 INFO Following table displays times when notifications are received
Time | Name | Node | Host:Port | Current State | Assigned State
---------+-------+-------+------------+---------------------+--------------------
14:57:16 | node2 | 1 | node2:5432 | primary | draining
14:57:16 | node1 | 2 | node1:5432 | secondary | prepare_promotion
14:57:16 | node1 | 2 | node1:5432 | prepare_promotion | prepare_promotion
14:57:16 | node1 | 2 | node1:5432 | prepare_promotion | stop_replication
14:57:16 | node2 | 1 | node2:5432 | primary | demote_timeout
14:57:17 | node2 | 1 | node2:5432 | draining | demote_timeout
14:57:17 | node2 | 1 | node2:5432 | demote_timeout | demote_timeout
14:57:19 | node1 | 2 | node1:5432 | stop_replication | stop_replication
14:57:19 | node1 | 2 | node1:5432 | stop_replication | wait_primary
14:57:19 | node2 | 1 | node2:5432 | demote_timeout | demoted
14:57:19 | node2 | 1 | node2:5432 | demoted | demoted
14:57:19 | node1 | 2 | node1:5432 | wait_primary | wait_primary
14:57:19 | node2 | 1 | node2:5432 | demoted | catchingup
14:57:26 | node2 | 1 | node2:5432 | demoted | catchingup
14:57:38 | node2 | 1 | node2:5432 | demoted | catchingup
14:57:39 | node2 | 1 | node2:5432 | catchingup | catchingup
14:57:39 | node2 | 1 | node2:5432 | catchingup | secondary
14:57:39 | node2 | 1 | node2:5432 | secondary | secondary
14:57:40 | node1 | 2 | node1:5432 | wait_primary | primary
14:57:40 | node1 | 2 | node1:5432 | primary | primary
The new state after the failover looks like the following:
$ docker-compose exec monitor pg_autoctl show state
Name | Node | Host:Port | TLI: LSN | Connection | Reported State | Assigned State
------+-------+------------+----------------+--------------+---------------------+--------------------
node2 | 1 | node2:5432 | 2: 0/5002698 | read-only | secondary | secondary
node1 | 2 | node1:5432 | 2: 0/5002698 | read-write | primary | primary
And we can verify that we still have the data available:
docker-compose exec app psql -c "select count(*) from companies"
count
-------
75
(1 row)
Multiple Standbys Architectures
The docker-compose.yml file comes with a third node that you can bring up to obtain the following
architecture:
[image: pg_auto_failover Architecture for a standalone PostgreSQL service] [image] pg_auto_failover
architecture with a primary and two standby nodes.UNINDENT
Adding a second standby node
To run a second standby node, or a third Postgres node, simply run the following command:
$ docker-compose up -d node3
We can see the resulting replication settings with the following command:
$ docker-compose exec monitor pg_autoctl show settings
Context | Name | Setting | Value
----------+---------+---------------------------+-------------------------------------------------------------
formation | default | number_sync_standbys | 1
primary | node1 | synchronous_standby_names | 'ANY 1 (pgautofailover_standby_1, pgautofailover_standby_3)'
node | node2 | candidate priority | 50
node | node1 | candidate priority | 50
node | node3 | candidate priority | 50
node | node2 | replication quorum | true
node | node1 | replication quorum | true
node | node3 | replication quorum | true
Editing the replication settings while in production
It's then possible to change the production architecture obtained with playing with the Replication
Settings and Postgres Architectures commands. Specifically, try the following command to change the
candidate_priority of the node3 to zero, in order for it to never be a candidate for failover:
$ docker-compose exec node3 pg_autoctl set candidate-priority 0 --name node3
To see the replication settings for all the nodes, the following command can be useful, and is described
in more details in the Replication Settings and Postgres Architectures section.
$ docker-compose exec monitor pg_autoctl show settings
Context | Name | Setting | Value
----------+---------+---------------------------+-------------------------------------------------------------
formation | default | number_sync_standbys | 1
primary | node1 | synchronous_standby_names | 'ANY 1 (pgautofailover_standby_1, pgautofailover_standby_3)'
node | node2 | candidate priority | 50
node | node1 | candidate priority | 50
node | node3 | candidate priority | 0
node | node2 | replication quorum | true
node | node1 | replication quorum | true
node | node3 | replication quorum | true
Then in a separate terminal (but in the same directory, because of the way docker-compose works with
projects), you can run the following watch command:
$ docker-compose exec monitor pg_autoctl watch
And in the main terminal, while the watch command output is visible, you can run a switchover operation:
$ docker-compose exec monitor pg_autoctl perform switchover
Getting familiar with those commands one of you next steps. The manual has coverage for them in the
following links:
• pg_autoctl watch
• pg_autoctl show state
• pg_autoctl show settings
• pg_autoctl set node candidate-priority
Cleanup
To dispose of the entire tutorial environment, just use the following command:
$ docker-compose down
Next steps
As mentioned in the first section of this tutorial, the way we use docker-compose here is not meant to be
production ready. It's useful to understand and play with a distributed system such as Postgres multiple
nodes system and failovers.
See the command pg_autoctl do tmux compose session for more details about how to run a docker-compose
test environment with docker-compose, including external volumes for each node.
See also the complete Azure VMs Tutorial for a guide on how-to provision an Azure network and then Azure
VMs with pg_auto_failover, including systemd coverage and a failover triggered by stopping a full VM.
AZURE VMS TUTORIAL
In this guide we’ll create a primary and secondary Postgres node and set up pg_auto_failover to replicate
data between them. We’ll simulate failure in the primary node and see how the system smoothly switches
(fails over) to the secondary.
For illustration, we'll run our databases on virtual machines in the Azure platform, but the techniques
here are relevant to any cloud provider or on-premise network. We'll use four virtual machines: a primary
database, a secondary database, a monitor, and an "application." The monitor watches the other nodes’
health, manages global state, and assigns nodes their roles.
Create virtual network
Our database machines need to talk to each other and to the monitor node, so let's create a virtual
network.
az group create \
--name ha-demo \
--location eastus
az network vnet create \
--resource-group ha-demo \
--name ha-demo-net \
--address-prefix 10.0.0.0/16
We need to open ports 5432 (Postgres) and 22 (SSH) between the machines, and also give ourselves access
from our remote IP. We'll do this with a network security group and a subnet.
az network nsg create \
--resource-group ha-demo \
--name ha-demo-nsg
az network nsg rule create \
--resource-group ha-demo \
--nsg-name ha-demo-nsg \
--name ha-demo-ssh-and-pg \
--access allow \
--protocol Tcp \
--direction Inbound \
--priority 100 \
--source-address-prefixes `curl ifconfig.me` 10.0.1.0/24 \
--source-port-range "*" \
--destination-address-prefix "*" \
--destination-port-ranges 22 5432
az network vnet subnet create \
--resource-group ha-demo \
--vnet-name ha-demo-net \
--name ha-demo-subnet \
--address-prefixes 10.0.1.0/24 \
--network-security-group ha-demo-nsg
Finally add four virtual machines (ha-demo-a, ha-demo-b, ha-demo-monitor, and ha-demo-app). For speed we
background the az vm create processes and run them in parallel:
# create VMs in parallel
for node in monitor a b app
do
az vm create \
--resource-group ha-demo \
--name ha-demo-${node} \
--vnet-name ha-demo-net \
--subnet ha-demo-subnet \
--nsg ha-demo-nsg \
--public-ip-address ha-demo-${node}-ip \
--image debian \
--admin-username ha-admin \
--generate-ssh-keys &
done
wait
To make it easier to SSH into these VMs in future steps, let's make a shell function to retrieve their IP
addresses:
# run this in your local shell as well
vm_ip () {
az vm list-ip-addresses -g ha-demo -n ha-demo-$1 -o tsv \
--query '[] [] .virtualMachine.network.publicIpAddresses[0].ipAddress'
}
# for convenience with ssh
for node in monitor a b app
do
ssh-keyscan -H `vm_ip $node` >> ~/.ssh/known_hosts
done
Let's review what we created so far.
az resource list --output table --query \
"[?resourceGroup=='ha-demo'].{ name: name, flavor: kind, resourceType: type, region: location }"
This shows the following resources:
Name ResourceType Region
------------------------------- ----------------------------------------------------- --------
ha-demo-a Microsoft.Compute/virtualMachines eastus
ha-demo-app Microsoft.Compute/virtualMachines eastus
ha-demo-b Microsoft.Compute/virtualMachines eastus
ha-demo-monitor Microsoft.Compute/virtualMachines eastus
ha-demo-appVMNic Microsoft.Network/networkInterfaces eastus
ha-demo-aVMNic Microsoft.Network/networkInterfaces eastus
ha-demo-bVMNic Microsoft.Network/networkInterfaces eastus
ha-demo-monitorVMNic Microsoft.Network/networkInterfaces eastus
ha-demo-nsg Microsoft.Network/networkSecurityGroups eastus
ha-demo-a-ip Microsoft.Network/publicIPAddresses eastus
ha-demo-app-ip Microsoft.Network/publicIPAddresses eastus
ha-demo-b-ip Microsoft.Network/publicIPAddresses eastus
ha-demo-monitor-ip Microsoft.Network/publicIPAddresses eastus
ha-demo-net Microsoft.Network/virtualNetworks eastus
Install the "pg_autoctl" executable
This guide uses Debian Linux, but similar steps will work on other distributions. All that differs are
the packages and paths. See Installing pg_auto_failover.
The pg_auto_failover system is distributed as a single pg_autoctl binary with subcommands to initialize
and manage a replicated PostgreSQL service. We’ll install the binary with the operating system package
manager on all nodes. It will help us run and observe PostgreSQL.
for node in monitor a b app
do
az vm run-command invoke \
--resource-group ha-demo \
--name ha-demo-${node} \
--command-id RunShellScript \
--scripts \
"sudo touch /home/ha-admin/.hushlogin" \
"curl https://install.citusdata.com/community/deb.sh | sudo bash" \
"sudo DEBIAN_FRONTEND=noninteractive apt-get install -q -y postgresql-common" \
"echo 'create_main_cluster = false' | sudo tee -a /etc/postgresql-common/createcluster.conf" \
"sudo DEBIAN_FRONTEND=noninteractive apt-get install -q -y postgresql-11-auto-failover-1.4" \
"sudo usermod -a -G postgres ha-admin" &
done
wait
Run a monitor
The pg_auto_failover monitor is the first component to run. It periodically attempts to contact the other
nodes and watches their health. It also maintains global state that “keepers” on each node consult to
determine their own roles in the system.
# on the monitor virtual machine
ssh -l ha-admin `vm_ip monitor` -- \
pg_autoctl create monitor \
--auth trust \
--ssl-self-signed \
--pgdata monitor \
--pgctl /usr/lib/postgresql/11/bin/pg_ctl
This command initializes a PostgreSQL cluster at the location pointed by the --pgdata option. When
--pgdata is omitted, pg_autoctl attempts to use the PGDATA environment variable. If a PostgreSQL instance
had already existing in the destination directory, this command would have configured it to serve as a
monitor.
pg_auto_failover, installs the pgautofailover Postgres extension, and grants access to a new autoctl_node
user.
In the Quick Start we use --auth trust to avoid complex security settings. The Postgres trust
authentication method is not considered a reasonable choice for production environments. Consider either
using the --skip-pg-hba option or --auth scram-sha-256 and then setting up passwords yourself.
At this point the monitor is created. Now we'll install it as a service with systemd so that it will
resume if the VM restarts.
ssh -T -l ha-admin `vm_ip monitor` << CMD
pg_autoctl -q show systemd --pgdata ~ha-admin/monitor > pgautofailover.service
sudo mv pgautofailover.service /etc/systemd/system
sudo systemctl daemon-reload
sudo systemctl enable pgautofailover
sudo systemctl start pgautofailover
CMD
Bring up the nodes
We’ll create the primary database using the pg_autoctl create subcommand.
ssh -l ha-admin `vm_ip a` -- \
pg_autoctl create postgres \
--pgdata ha \
--auth trust \
--ssl-self-signed \
--username ha-admin \
--dbname appdb \
--hostname ha-demo-a.internal.cloudapp.net \
--pgctl /usr/lib/postgresql/11/bin/pg_ctl \
--monitor 'postgres://autoctl_node@ha-demo-monitor.internal.cloudapp.net/pg_auto_failover?sslmode=require'
Notice the user and database name in the monitor connection string -- these are what monitor init
created. We also give it the path to pg_ctl so that the keeper will use the correct version of pg_ctl in
future even if other versions of postgres are installed on the system.
In the example above, the keeper creates a primary database. It chooses to set up node A as primary
because the monitor reports there are no other nodes in the system yet. This is one example of how the
keeper is state-based: it makes observations and then adjusts its state, in this case from "init" to
"single."
Also add a setting to trust connections from our "application" VM:
ssh -T -l ha-admin `vm_ip a` << CMD
echo 'hostssl "appdb" "ha-admin" ha-demo-app.internal.cloudapp.net trust' \
>> ~ha-admin/ha/pg_hba.conf
CMD
At this point the monitor and primary node are created and running. Next we need to run the keeper. It’s
an independent process so that it can continue operating even if the PostgreSQL process goes terminates
on the node. We'll install it as a service with systemd so that it will resume if the VM restarts.
ssh -T -l ha-admin `vm_ip a` << CMD
pg_autoctl -q show systemd --pgdata ~ha-admin/ha > pgautofailover.service
sudo mv pgautofailover.service /etc/systemd/system
sudo systemctl daemon-reload
sudo systemctl enable pgautofailover
sudo systemctl start pgautofailover
CMD
Next connect to node B and do the same process. We'll do both steps at once:
ssh -l ha-admin `vm_ip b` -- \
pg_autoctl create postgres \
--pgdata ha \
--auth trust \
--ssl-self-signed \
--username ha-admin \
--dbname appdb \
--hostname ha-demo-b.internal.cloudapp.net \
--pgctl /usr/lib/postgresql/11/bin/pg_ctl \
--monitor 'postgres://autoctl_node@ha-demo-monitor.internal.cloudapp.net/pg_auto_failover?sslmode=require'
ssh -T -l ha-admin `vm_ip b` << CMD
pg_autoctl -q show systemd --pgdata ~ha-admin/ha > pgautofailover.service
sudo mv pgautofailover.service /etc/systemd/system
sudo systemctl daemon-reload
sudo systemctl enable pgautofailover
sudo systemctl start pgautofailover
CMD
It discovers from the monitor that a primary exists, and then switches its own state to be a hot standby
and begins streaming WAL contents from the primary.
Node communication
For convenience, pg_autoctl modifies each node's pg_hba.conf file to allow the nodes to connect to one
another. For instance, pg_autoctl added the following lines to node A:
# automatically added to node A
hostssl "appdb" "ha-admin" ha-demo-a.internal.cloudapp.net trust
hostssl replication "pgautofailover_replicator" ha-demo-b.internal.cloudapp.net trust
hostssl "appdb" "pgautofailover_replicator" ha-demo-b.internal.cloudapp.net trust
For pg_hba.conf on the monitor node pg_autoctl inspects the local network and makes its best guess about
the subnet to allow. In our case it guessed correctly:
# automatically added to the monitor
hostssl "pg_auto_failover" "autoctl_node" 10.0.1.0/24 trust
If worker nodes have more ad-hoc addresses and are not in the same subnet, it's better to disable
pg_autoctl's automatic modification of pg_hba using the --skip-pg-hba command line option during
creation. You will then need to edit the hba file by hand. Another reason for manual edits would be to
use special authentication methods.
Watch the replication
First let’s verify that the monitor knows about our nodes, and see what states it has assigned them:
ssh -l ha-admin `vm_ip monitor` pg_autoctl show state --pgdata monitor
Name | Node | Host:Port | LSN | Reachable | Current State | Assigned State
-------+-------+--------------------------------------+-----------+-----------+---------------------+--------------------
node_1 | 1 | ha-demo-a.internal.cloudapp.net:5432 | 0/3000060 | yes | primary | primary
node_2 | 2 | ha-demo-b.internal.cloudapp.net:5432 | 0/3000060 | yes | secondary | secondary
This looks good. We can add data to the primary, and later see it appear in the secondary. We'll connect
to the database from inside our "app" virtual machine, using a connection string obtained from the
monitor.
ssh -l ha-admin `vm_ip monitor` pg_autoctl show uri --pgdata monitor
Type | Name | Connection String
-----------+---------+-------------------------------
monitor | monitor | postgres://autoctl_node@ha-demo-monitor.internal.cloudapp.net:5432/pg_auto_failover?sslmode=require
formation | default | postgres://ha-demo-b.internal.cloudapp.net:5432,ha-demo-a.internal.cloudapp.net:5432/appdb?target_session_attrs=read-write&sslmode=require
Now we'll get the connection string and store it in a local environment variable:
APP_DB_URI=$( \
ssh -l ha-admin `vm_ip monitor` \
pg_autoctl show uri --formation default --pgdata monitor \
)
The connection string contains both our nodes, comma separated, and includes the url parameter
?target_session_attrs=read-write telling psql that we want to connect to whichever of these servers
supports reads and writes. That will be the primary server.
# connect to database via psql on the app vm and
# create a table with a million rows
ssh -l ha-admin -t `vm_ip app` -- \
psql "'$APP_DB_URI'" \
-c "'CREATE TABLE foo AS SELECT generate_series(1,1000000) bar;'"
Cause a failover
Now that we've added data to node A, let's switch which is considered the primary and which the
secondary. After the switch we'll connect again and query the data, this time from node B.
# initiate failover to node B
ssh -l ha-admin -t `vm_ip monitor` \
pg_autoctl perform switchover --pgdata monitor
Once node B is marked "primary" (or "wait_primary") we can connect and verify that the data is still
present:
# connect to database via psql on the app vm
ssh -l ha-admin -t `vm_ip app` -- \
psql "'$APP_DB_URI'" \
-c "'SELECT count(*) FROM foo;'"
It shows
count
---------
1000000
Cause a node failure
This plot is too boring, time to introduce a problem. We’ll turn off VM for node B (currently the primary
after our previous failover) and watch node A get promoted.
In one terminal let’s keep an eye on events:
ssh -t -l ha-admin `vm_ip monitor` -- \
watch -n 1 -d pg_autoctl show state --pgdata monitor
In another terminal we’ll turn off the virtual server.
az vm stop \
--resource-group ha-demo \
--name ha-demo-b
After a number of failed attempts to talk to node B, the monitor determines the node is unhealthy and
puts it into the "demoted" state. The monitor promotes node A to be the new primary.
Name | Node | Host:Port | LSN | Reachable | Current State | Assigned State
-------+-------+--------------------------------------+-----------+-----------+---------------------+--------------------
node_1 | 1 | ha-demo-a.internal.cloudapp.net:5432 | 0/6D4E068 | yes | wait_primary | wait_primary
node_2 | 2 | ha-demo-b.internal.cloudapp.net:5432 | 0/6D4E000 | yes | demoted | catchingup
Node A cannot be considered in full "primary" state since there is no secondary present, but it can still
serve client requests. It is marked as "wait_primary" until a secondary appears, to indicate that it's
running without a backup.
Let's add some data while B is offline.
# notice how $APP_DB_URI continues to work no matter which node
# is serving as primary
ssh -l ha-admin -t `vm_ip app` -- \
psql "'$APP_DB_URI'" \
-c "'INSERT INTO foo SELECT generate_series(1000001, 2000000);'"
Resurrect node B
Run this command to bring node B back online:
az vm start \
--resource-group ha-demo \
--name ha-demo-b
Now the next time the keeper retries its health check, it brings the node back. Node B goes through the
state "catchingup" while it updates its data to match A. Once that's done, B becomes a secondary, and A
is now a full primary again.
Name | Node | Host:Port | LSN | Reachable | Current State | Assigned State
-------+-------+--------------------------------------+------------+-----------+---------------------+--------------------
node_1 | 1 | ha-demo-a.internal.cloudapp.net:5432 | 0/12000738 | yes | primary | primary
node_2 | 2 | ha-demo-b.internal.cloudapp.net:5432 | 0/12000738 | yes | secondary | secondary
What's more, if we connect directly to the database again, all two million rows are still present.
ssh -l ha-admin -t `vm_ip app` -- \
psql "'$APP_DB_URI'" \
-c "'SELECT count(*) FROM foo;'"
It shows
count
---------
2000000
INSTALLING PG_AUTO_FAILOVER
We provide native system packages for pg_auto_failover on most popular Linux distributions.
Use the steps below to install pg_auto_failover on PostgreSQL 11. At the current time pg_auto_failover is
compatible with both PostgreSQL 10 and PostgreSQL 11.
Ubuntu or Debian
Postgres apt repository
Binary packages for debian and derivatives (ubuntu) are available from apt.postgresql.org repository,
install by following the linked documentation and then:
$ sudo apt-get install pg-auto-failover-cli
$ sudo apt-get install postgresql-14-auto-failover
The Postgres extension named "pgautofailover" is only necessary on the monitor node. To install that
extension, you can install the postgresql-14-auto-failover package when using Postgres 14. It's available
for other Postgres versions too.
Avoiding the default Postgres service
When installing the debian Postgres package, the installation script will initialize a Postgres data
directory automatically, and register it to the systemd services. When using pg_auto_failover, it is best
to avoid that step.
To avoid automated creation of a Postgres data directory when installing the debian package, follow those
steps:
$ curl https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add -
$ echo "deb http://apt.postgresql.org/pub/repos/apt buster-pgdg main" > /etc/apt/sources.list.d/pgdg.list
# bypass initdb of a "main" cluster
$ echo 'create_main_cluster = false' | sudo tee -a /etc/postgresql-common/createcluster.conf
$ apt-get update
$ apt-get install -y --no-install-recommends postgresql-14
That way when it's time to pg_autoctl create monitor or pg_autoctl create postgres there is no confusion
about how to handle the default Postgres service created by debian: it has not been created at all.
Fedora, CentOS, or Red Hat
The Postgres community packaging team for RPM based system has worked on supporting pg_auto_failover.
Binary packages are available by following the documentation at PostgreSQL Yum Repository.
A single package named pg_auto_failover is available on the RPM based systems, containing both the
monitor Postgres extension and the pg_autoctl command line.
Installing a pgautofailover Systemd unit
The command pg_autoctl show systemd outputs a systemd unit file that you can use to setup a boot-time
registered service for pg_auto_failover on your machine.
Here's a sample output from the command:
$ export PGDATA=/var/lib/postgresql/monitor
$ pg_autoctl show systemd
13:44:34 INFO HINT: to complete a systemd integration, run the following commands:
13:44:34 INFO pg_autoctl -q show systemd --pgdata "/var/lib/postgresql/monitor" | sudo tee /etc/systemd/system/pgautofailover.service
13:44:34 INFO sudo systemctl daemon-reload
13:44:34 INFO sudo systemctl start pgautofailover
[Unit]
Description = pg_auto_failover
[Service]
WorkingDirectory = /var/lib/postgresql
Environment = 'PGDATA=/var/lib/postgresql/monitor'
User = postgres
ExecStart = /usr/lib/postgresql/10/bin/pg_autoctl run
Restart = always
StartLimitBurst = 0
[Install]
WantedBy = multi-user.target
Copy/pasting the commands given in the hint output from the command will enable the pgautofailer service
on your system, when using systemd.
It is important that PostgreSQL is started by pg_autoctl rather than by systemd itself, as it might be
that a failover has been done during a reboot, for instance, and that once the reboot complete we want
the local Postgres to re-join as a secondary node where it used to be a primary node.
Building pg_auto_failover from sources
To build the project, make sure you have installed the build-dependencies, then just type make. You can
install the resulting binary using make install.
For this to work please consider adding both the binary and the source repositories to your debian
distribution by using the following apt sources, as an example targetting the debian bullseye
distribution:
deb http://apt.postgresql.org/pub/repos/apt bullseye-pgdg main
deb-src http://apt.postgresql.org/pub/repos/apt bullseye-pgdg main
Then we can install the build dependencies for Postgres, knowing that pg_auto_failover uses the same
build dependencies:
$ sudo apt-get build-dep -y --no-install-recommends postgresql-14
Then build pg_auto_failover from sources with the following instructions:
$ make -s clean && make -s -j12 all
$ sudo make -s install
ARCHITECTURE BASICS
pg_auto_failover is designed as a simple and robust way to manage automated Postgres failover in
production. On-top of robust operations, pg_auto_failover setup is flexible and allows either Business
Continuity or High Availability configurations. pg_auto_failover design includes configuration changes in
a live system without downtime.
pg_auto_failover is designed to be able to handle a single PostgreSQL service using three nodes. In this
setting, the system is resilient to losing any one of three nodes.
[image: pg_auto_failover Architecture for a standalone PostgreSQL service] [image] pg_auto_failover
Architecture for a standalone PostgreSQL service.UNINDENT
It is important to understand that when using only two Postgres nodes then pg_auto_failover is
optimized for Business Continuity. In the event of losing a single node, pg_auto_failover is capable of
continuing the PostgreSQL service, and prevents any data loss when doing so, thanks to PostgreSQL
Synchronous Replication.
That said, there is a trade-off involved in this architecture. The business continuity bias relaxes
replication guarantees for asynchronous replication in the event of a standby node failure. This allows
the PostgreSQL service to accept writes when there's a single server available, and opens the service
for potential data loss if the primary server were also to fail.
The pg_auto_failover Monitor
Each PostgreSQL node in pg_auto_failover runs a Keeper process which informs a central Monitor node about
notable local changes. Some changes require the Monitor to orchestrate a correction across the cluster:
• New nodes
At initialization time, it's necessary to prepare the configuration of each node for PostgreSQL
streaming replication, and get the cluster to converge to the nominal state with both a primary and
a secondary node in each group. The monitor determines each new node's role
• Node failure
The monitor orchestrates a failover when it detects an unhealthy node. The design of
pg_auto_failover allows the monitor to shut down service to a previously designated primary node
without causing a "split-brain" situation.
The monitor is the authoritative node that manages global state and makes changes in the cluster by
issuing commands to the nodes' keeper processes. A pg_auto_failover monitor node failure has limited
impact on the system. While it prevents reacting to other nodes' failures, it does not affect
replication. The PostgreSQL streaming replication setup installed by pg_auto_failover does not depend on
having the monitor up and running.
pg_auto_failover Glossary
pg_auto_failover handles a single PostgreSQL service with the following concepts:
Monitor
The pg_auto_failover monitor is a service that keeps track of one or several formations containing groups
of nodes.
The monitor is implemented as a PostgreSQL extension, so when you run the command pg_autoctl create
monitor a PostgreSQL instance is initialized, configured with the extension, and started. The monitor
service embeds a PostgreSQL instance.
Formation
A formation is a logical set of PostgreSQL services that are managed together.
It is possible to operate many formations with a single monitor instance. Each formation has a group of
Postgres nodes and the FSM orchestration implemented by the monitor applies separately to each group.
Group
A group of two PostgreSQL nodes work together to provide a single PostgreSQL service in a Highly
Available fashion. A group consists of a PostgreSQL primary server and a secondary server setup with Hot
Standby synchronous replication. Note that pg_auto_failover can orchestrate the whole setting-up of the
replication for you.
In pg_auto_failover versions up to 1.3, a single Postgres group can contain only two Postgres nodes.
Starting with pg_auto_failover 1.4, there's no limit to the number of Postgres nodes in a single group.
Note that each Postgres instance that belongs to the same group serves the same dataset in its data
directory (PGDATA).
NOTE:
The notion of a formation that contains multiple groups in pg_auto_failover is useful when setting up
and managing a whole Citus formation, where the coordinator nodes belong to group zero of the
formation, and each Citus worker node becomes its own group and may have Postgres standby nodes.
Keeper
The pg_auto_failover keeper is an agent that must be running on the same server where your PostgreSQL
nodes are running. The keeper controls the local PostgreSQL instance (using both the pg_ctl command-line
tool and SQL queries), and communicates with the monitor:
• it sends updated data about the local node, such as the WAL delta in between servers, measured via
PostgreSQL statistics views.
• it receives state assignments from the monitor.
Also the keeper maintains local state that includes the most recent communication established with the
monitor and the other PostgreSQL node of its group, enabling it to detect Network Partitions.
NOTE:
In pg_auto_failover versions up to and including 1.3, the keeper process started with pg_autoctl run
manages a separate Postgres instance, running as its own process tree.
Starting in pg_auto_failover version 1.4, the keeper process (started with pg_autoctl run) runs the
Postgres instance as a sub-process of the main pg_autoctl process, allowing tighter control over the
Postgres execution. Running the sub-process also makes the solution work better both in container
environments (because it's now a single process tree) and with systemd, because it uses a specific
cgroup per service unit.
Node
A node is a server (virtual or physical) that runs PostgreSQL instances and a keeper service. At any
given time, any node might be a primary or a secondary Postgres instance. The whole point of
pg_auto_failover is to decide this state.
As a result, refrain from naming your nodes with the role you intend for them. Their roles can change.
If they didn't, your system wouldn't need pg_auto_failover!
State
A state is the representation of the per-instance and per-group situation. The monitor and the keeper
implement a Finite State Machine to drive operations in the PostgreSQL groups; allowing pg_auto_failover
to implement High Availability with the goal of zero data loss.
The keeper main loop enforces the current expected state of the local PostgreSQL instance, and reports
the current state and some more information to the monitor. The monitor uses this set of information and
its own health-check information to drive the State Machine and assign a goal state to the keeper.
The keeper implements the transitions between a current state and a monitor-assigned goal state.
Client-side HA
Implementing client-side High Availability is included in PostgreSQL's driver libpq from version 10
onward. Using this driver, it is possible to specify multiple host names or IP addresses in the same
connection string:
$ psql -d "postgresql://host1,host2/dbname?target_session_attrs=read-write"
$ psql -d "postgresql://host1:port2,host2:port2/dbname?target_session_attrs=read-write"
$ psql -d "host=host1,host2 port=port1,port2 target_session_attrs=read-write"
When using either of the syntax above, the psql application attempts to connect to host1, and when
successfully connected, checks the target_session_attrs as per the PostgreSQL documentation of it:
If this parameter is set to read-write, only a connection in which read-write transactions are
accepted by default is considered acceptable. The query SHOW transaction_read_only will be sent upon
any successful connection; if it returns on, the connection will be closed. If multiple hosts were
specified in the connection string, any remaining servers will be tried just as if the connection
attempt had failed. The default value of this parameter, any, regards all connections as acceptable.
When the connection attempt to host1 fails, or when the target_session_attrs can not be verified, then
the psql application attempts to connect to host2.
The behavior is implemented in the connection library libpq, so any application using it can benefit from
this implementation, not just psql.
When using pg_auto_failover, configure your application connection string to use the primary and the
secondary server host names, and set target_session_attrs=read-write too, so that your application
automatically connects to the current primary, even after a failover occurred.
Monitoring protocol
The monitor interacts with the data nodes in 2 ways:
• Data nodes periodically connect and run SELECT pgautofailover.node_active(...) to communicate their
current state and obtain their goal state.
• The monitor periodically connects to all the data nodes to see if they are healthy, doing the
equivalent of pg_isready.
When a data node calls node_active, the state of the node is stored in the pgautofailover.node table and
the state machines of both nodes are progressed. The state machines are described later in this readme.
The monitor typically only moves one state forward and waits for the node(s) to converge except in
failure states.
If a node is not communicating to the monitor, it will either cause a failover (if node is a primary),
disabling synchronous replication (if node is a secondary), or cause the state machine to pause until the
node comes back (other cases). In most cases, the latter is harmless, though in some cases it may cause
downtime to last longer, e.g. if a standby goes down during a failover.
To simplify operations, a node is only considered unhealthy if the monitor cannot connect and it hasn't
reported its state through node_active for a while. This allows, for example, PostgreSQL to be restarted
without causing a health check failure.
Synchronous vs. asynchronous replication
By default, pg_auto_failover uses synchronous replication, which means all writes block until at least
one standby node has reported receiving them. To handle cases in which the standby fails, the primary
switches between two states called wait_primary and primary based on the health of standby nodes, and
based on the replication setting number_sync_standby.
When in the wait_primary state, synchronous replication is disabled by automatically setting
synchronous_standby_names = '' to allow writes to proceed. However doing so also disables failover, since
the standby might get arbitrarily far behind. If the standby is responding to health checks and within 1
WAL segment of the primary (by default), synchronous replication is enabled again on the primary by
setting synchronous_standby_names = '*' which may cause a short latency spike since writes will then
block until the standby has caught up.
When using several standby nodes with replication quorum enabled, the actual setting for
synchronous_standby_names is set to a list of those standby nodes that are set to participate to the
replication quorum.
If you wish to disable synchronous replication, you need to add the following to postgresql.conf:
synchronous_commit = 'local'
This ensures that writes return as soon as they are committed on the primary -- under all circumstances.
In that case, failover might lead to some data loss, but failover is not initiated if the secondary is
more than 10 WAL segments (by default) behind on the primary. During a manual failover, the standby will
continue accepting writes from the old primary. The standby will stop accepting writes only if it's fully
caught up (most common), the primary fails, or it does not receive writes for 2 minutes.
A note about performance
In some cases the performance impact on write latency when setting synchronous replication makes the
application fail to deliver expected performance. If testing or production feedback shows this to be the
case, it is beneficial to switch to using asynchronous replication.
The way to use asynchronous replication in pg_auto_failover is to change the synchronous_commit setting.
This setting can be set per transaction, per session, or per user. It does not have to be set globally on
your Postgres instance.
One way to benefit from that would be:
alter role fast_and_loose set synchronous_commit to local;
That way performance-critical parts of the application don't have to wait for the standby nodes. Only use
this when you can also lower your data durability guarantees.
Node recovery
When bringing a node back after a failover, the keeper (pg_autoctl run) can simply be restarted. It will
also restart postgres if needed and obtain its goal state from the monitor. If the failed node was a
primary and was demoted, it will learn this from the monitor. Once the node reports, it is allowed to
come back as a standby by running pg_rewind. If it is too far behind, the node performs a new
pg_basebackup.
MULTI-NODE ARCHITECTURES
Pg_auto_failover allows you to have more than one standby node, and offers advanced control over your
production architecture characteristics.
Architectures with two standby nodes
When adding your second standby node with default settings, you get the following architecture:
[image: pg_auto_failover architecture with two standby nodes] [image] pg_auto_failover architecture
with two standby nodes.UNINDENT
In this case, three nodes get set up with the same characteristics, achieving HA for both the Postgres
service and the production dataset. An important setting for this architecture is number_sync_standbys.
The replication setting number_sync_standbys sets how many standby nodes the primary should wait for
when committing a transaction. In order to have a good availability in your system, pg_auto_failover
requires number_sync_standbys + 1 standby nodes participating in the replication quorum: this allows
any standby node to fail without impact on the system's ability to respect the replication quorum.
When only two nodes are registered in a group on the monitor we have a primary and a single secondary
node. Then number_sync_standbys can only be set to zero. When adding a second standby node to a
pg_auto_failover group, then the monitor automatically increments number_sync_standbys to one, as we
see in the diagram above.
When number_sync_standbys is set to zero then pg_auto_failover implements the Business Continuity setup
as seen in Architecture Basics: synchronous replication is then used as a way to guarantee that
failover can be implemented without data loss.
In more details:
1. With number_sync_standbys set to one, this architecture always maintains two copies of the dataset:
one on the current primary node (node A in the previous diagram), and one on the standby that
acknowledges the transaction first (either node B or node C in the diagram).
When one of the standby nodes is unavailable, the second copy of the dataset can still be
maintained thanks to the remaining standby.
When both the standby nodes are unavailable, then it's no longer possible to guarantee the
replication quorum, and thus writes on the primary are blocked. The Postgres primary node waits
until at least one standby node acknowledges the transactions locally committed, thus degrading
your Postgres service to read-only.
0. It is possible to manually set number_sync_standbys to zero when having registered two standby
nodes to the monitor, overriding the default behavior.
In that case, when the second standby node becomes unhealthy at the same time as the first standby
node, the primary node is assigned the state Wait_primary. In that state, synchronous replication
is disabled on the primary by setting synchronous_standby_names to an empty string. Writes are
allowed on the primary, even though there's no extra copy of the production dataset available at
this time.
Setting number_sync_standbys to zero allows data to be written even when both standby nodes are
down. In this case, a single copy of the production data set is kept and, if the primary was then
to fail, some data will be lost. How much depends on your backup and recovery mechanisms.
Replication Settings and Postgres Architectures
The entire flexibility of pg_auto_failover can be leveraged with the following three replication
settings:
• Number of sync stanbys
• Replication quorum
• Candidate priority
Number Sync Standbys
This parameter is used by Postgres in the synchronous_standby_names parameter: number_sync_standby is the
number of synchronous standbys for whose replies transactions must wait.
This parameter can be set at the formation level in pg_auto_failover, meaning that it applies to the
current primary, and "follows" a failover to apply to any new primary that might replace the current one.
To set this parameter to the value <n>, use the following command:
pg_autoctl set formation number-sync-standbys <n>
The default value in pg_auto_failover is zero. When set to zero, the Postgres parameter
synchronous_standby_names can be set to either '*' or to '':
• synchronous_standby_names = '*' means that any standby may participate in the replication quorum for
transactions with synchronous_commit set to on or higher values.
pg_autofailover uses synchronous_standby_names = '*' when there's at least one standby that is known to
be healthy.
• synchronous_standby_names = '' (empty string) disables synchrous commit and makes all your commits
asynchronous, meaning that transaction commits will not wait for replication. In other words, a single
copy of your production data is maintained when synchronous_standby_names is set that way.
pg_autofailover uses synchronous_standby_names = '' only when number_sync_standbys is set to zero and
there's no standby node known healthy by the monitor.
In order to set number_sync_standbys to a non-zero value, pg_auto_failover requires that at least
number_sync_standbys + 1 standby nodes be registered in the system.
When the first standby node is added to the pg_auto_failover monitor, the only acceptable value for
number_sync_standbys is zero. When a second standby is added that participates in the replication quorum,
then number_sync_standbys is automatically set to one.
The command pg_autoctl set formation number-sync-standbys can be used to change the value of this
parameter in a formation, even when all the nodes are already running in production. The pg_auto_failover
monitor then sets a transition for the primary to update its local value of synchronous_standby_names.
Replication Quorum
The replication quorum setting is a boolean and defaults to true, and can be set per-node.
Pg_auto_failover includes a given node in synchronous_standby_names only when the replication quorum
parameter has been set to true. This means that asynchronous replication will be used for nodes where
replication-quorum is set to false.
It is possible to force asynchronous replication globally by setting replication quorum to false on all
the nodes in a formation. Remember that failovers will happen, and thus to set your replication settings
on the current primary node too when needed: it is going to be a standby later.
To set this parameter to either true or false, use one of the following commands:
pg_autoctl set node replication-quorum true
pg_autoctl set node replication-quorum false
Candidate Priority
The candidate priority setting is an integer that can be set to any value between 0 (zero) and 100 (one
hundred). The default value is 50. When the pg_auto_failover monitor decides to orchestrate a failover,
it uses each node's candidate priority to pick the new primary node.
When setting the candidate priority of a node down to zero, this node will never be selected to be
promoted as the new primary when a failover is orchestrated by the monitor. The monitor will instead wait
until another node registered is healthy and in a position to be promoted.
To set this parameter to the value <n>, use the following command:
pg_autoctl set node candidate-priority <n>
When nodes have the same candidate priority, the monitor then picks the standby with the most advanced
LSN position published to the monitor. When more than one node has published the same LSN position, a
random one is chosen.
When the candidate for failover has not published the most advanced LSN position in the WAL,
pg_auto_failover orchestrates an intermediate step in the failover mechanism. The candidate fetches the
missing WAL bytes from one of the standby with the most advanced LSN position prior to being promoted.
Postgres allows this operation thanks to cascading replication: any standby can be the upstream node for
another standby.
It is required at all times that at least two nodes have a non-zero candidate priority in any
pg_auto_failover formation. Otherwise no failover is possible.
Auditing replication settings
The command pg_autoctl get formation settings (also known as pg_autoctl show settings) can be used to
obtain a summary of all the replication settings currently in effect in a formation. Still using the
first diagram on this page, we get the following summary:
$ pg_autoctl get formation settings
Context | Name | Setting | Value
----------+---------+---------------------------+-------------------------------------------------------------
formation | default | number_sync_standbys | 1
primary | node_A | synchronous_standby_names | 'ANY 1 (pgautofailover_standby_3, pgautofailover_standby_2)'
node | node_A | replication quorum | true
node | node_B | replication quorum | true
node | node_C | replication quorum | true
node | node_A | candidate priority | 50
node | node_B | candidate priority | 50
node | node_C | candidate priority | 50
We can see that the number_sync_standbys has been used to compute the current value of the
synchronous_standby_names setting on the primary.
Because all the nodes in that example have the same default candidate priority (50), then
pg_auto_failover is using the form ANY 1 with the list of standby nodes that are currently participating
in the replication quorum.
The entries in the synchronous_standby_names list are meant to match the application_name connection
setting used in the primary_conninfo, and the format used by pg_auto_failover there is the format string
"pgautofailover_standby_%d" where %d is replaced by the node id. This allows keeping the same connection
string to the primary when the node name is changed (using the command pg_autoctl set metadata --name).
Here we can see the node id of each registered Postgres node with the following command:
$ pg_autoctl show state
Name | Node | Host:Port | LSN | Reachable | Current State | Assigned State
-------+-------+----------------+-----------+-----------+---------------------+--------------------
node_A | 1 | localhost:5001 | 0/7002310 | yes | primary | primary
node_B | 2 | localhost:5002 | 0/7002310 | yes | secondary | secondary
node_C | 3 | localhost:5003 | 0/7002310 | yes | secondary | secondary
When setting pg_auto_failover with per formation number_sync_standby and then per node replication quorum
and candidate priority replication settings, those properties are then used to compute the
synchronous_standby_names value on the primary node. This value is automatically maintained on the
primary by pg_auto_failover, and is updated either when replication settings are changed or when a
failover happens.
The other situation when the pg_auto_failover replication settings are used is a candidate election when
a failover happens and there is more than two nodes registered in a group. Then the node with the highest
candidate priority is selected, as detailed above in the Candidate Priority section.
Sample architectures with three standby nodes
When setting the three parameters above, it's possible to design very different Postgres architectures
for your production needs.
[image: pg_auto_failover architecture with three standby nodes] [image] pg_auto_failover architecture
with three standby nodes.UNINDENT
In this case, the system is set up with three standby nodes all set the same way, with default
parameters. The default parameters support setting number_sync_standbys = 2. This means that Postgres
will maintain three copies of the production data set at all times.
On the other hand, if two standby nodes were to fail at the same time, despite the fact that two copies
of the data are still maintained, the Postgres service would be degraded to read-only.
With this architecture diagram, here's the summary that we obtain:
$ pg_autoctl show settings
Context | Name | Setting | Value
----------+---------+---------------------------+---------------------------------------------------------------------------------------
formation | default | number_sync_standbys | 2
primary | node_A | synchronous_standby_names | 'ANY 2 (pgautofailover_standby_2, pgautofailover_standby_4, pgautofailover_standby_3)'
node | node_A | replication quorum | true
node | node_B | replication quorum | true
node | node_C | replication quorum | true
node | node_D | replication quorum | true
node | node_A | candidate priority | 50
node | node_B | candidate priority | 50
node | node_C | candidate priority | 50
node | node_D | candidate priority | 50
Sample architecture with three standby nodes, one async
[image: pg_auto_failover architecture with three standby nodes, one async] [image] pg_auto_failover
architecture with three standby nodes, one async.UNINDENT
In this case, the system is set up with two standby nodes participating in the replication quorum,
allowing for number_sync_standbys = 1. The system always maintains at least two copies of the data set,
one on the primary, another on either node B or node C. Whenever we lose one of those nodes, we can
hold to the guarantee of having two copies of the data set.
Additionally, we have the standby server D which has been set up to not participate in the replication
quorum. Node D will not be found in the synchronous_standby_names list of nodes. Also, node D is set up
to never be a candidate for failover, with candidate-priority = 0.
This architecture would fit a situation with nodes A, B, and C are deployed in the same data center or
availability zone and node D in another one. Those three nodes are set up to support the main
production traffic and implement high availability of both the Postgres service and the data set.
Node D might be set up for Business Continuity in case the first data center is lost, or maybe for
reporting needs on another application domain.
With this architecture diagram, here's the summary that we obtain:
pg_autoctl show settings
Context | Name | Setting | Value
----------+---------+---------------------------+-------------------------------------------------------------
formation | default | number_sync_standbys | 1
primary | node_A | synchronous_standby_names | 'ANY 1 (pgautofailover_standby_2, pgautofailover_standby_3)'
node | node_A | replication quorum | true
node | node_B | replication quorum | true
node | node_C | replication quorum | true
node | node_D | replication quorum | false
node | node_A | candidate priority | 50
node | node_B | candidate priority | 50
node | node_C | candidate priority | 50
node | node_D | candidate priority | 0
FAILOVER STATE MACHINE
Introduction
pg_auto_failover uses a state machine for highly controlled execution. As keepers inform the monitor
about new events (or fail to contact it at all), the monitor assigns each node both a current state and a
goal state. A node's current state is a strong guarantee of its capabilities. States themselves do not
cause any actions; actions happen during state transitions. The assigned goal states inform keepers of
what transitions to attempt.
Example of state transitions in a new cluster
A good way to get acquainted with the states is by examining the transitions of a cluster from birth to
high availability.
After starting a monitor and running keeper init for the first data node ("node A"), the monitor
registers the state of that node as "init" with a goal state of "single." The init state means the
monitor knows nothing about the node other than its existence because the keeper is not yet continuously
running there to report node health.
Once the keeper runs and reports its health to the monitor, the monitor assigns it the state "single,"
meaning it is just an ordinary Postgres server with no failover. Because there are not yet other nodes in
the cluster, the monitor also assigns node A the goal state of single -- there's nothing that node A's
keeper needs to change.
As soon as a new node ("node B") is initialized, the monitor assigns node A the goal state of
"wait_primary." This means the node still has no failover, but there's hope for a secondary to
synchronize with it soon. To accomplish the transition from single to wait_primary, node A's keeper adds
node B's hostname to pg_hba.conf to allow a hot standby replication connection.
At the same time, node B transitions into wait_standby with the goal initially of staying in
wait_standby. It can do nothing but wait until node A gives it access to connect. Once node A has
transitioned to wait_primary, the monitor assigns B the goal of "catchingup," which gives B's keeper the
green light to make the transition from wait_standby to catchingup. This transition involves running
pg_basebackup, editing recovery.conf and restarting PostgreSQL in Hot Standby node.
Node B reports to the monitor when it's in hot standby mode and able to connect to node A. The monitor
then assigns node B the goal state of "secondary" and A the goal of "primary." Postgres ships WAL logs
from node A and replays them on B. Finally B is caught up and tells the monitor (specifically B reports
its pg_stat_replication.sync_state and WAL replay lag). At this glorious moment the monitor assigns A the
state primary (goal: primary) and B secondary (goal: secondary).
State reference
The following diagram shows the pg_auto_failover State Machine. It's missing links to the single state,
which can always been reached when removing all the other nodes.
[image: pg_auto_failover Finite State Machine diagram] [image] pg_auto_failover Finite State Machine
diagram.UNINDENT
In the previous diagram we can see that we have a list of six states where the application can connect
to a read-write Postgres service: single, wait_primary, primary, prepare_maintenance, and
apply_settings.
Init
A node is assigned the "init" state when it is first registered with the monitor. Nothing is known about
the node at this point beyond its existence. If no other node has been registered with the monitor for
the same formation and group ID then this node is assigned a goal state of "single." Otherwise the node
has the goal state of "wait_standby."
Single
There is only one node in the group. It behaves as a regular PostgreSQL instance, with no high
availability and no failover. If the administrator removes a node the other node will revert to the
single state.
Wait_primary
Applied to a node intended to be the primary but not yet in that position. The primary-to-be at this
point knows the secondary's node name or IP address, and has granted the node hot standby access in the
pg_hba.conf file.
The wait_primary state may be caused either by a new potential secondary being registered with the
monitor (good), or an existing secondary becoming unhealthy (bad). In the latter case, during the
transition from primary to wait_primary, the primary node's keeper disables synchronous replication on
the node. It also cancels currently blocked queries.
Join_primary
Applied to a primary node when another standby is joining the group. This allows the primary node to
apply necessary changes to its HBA setup before allowing the new node joining the system to run the
pg_basebackup command.
IMPORTANT:
This state has been deprecated, and is no longer assigned to nodes. Any time we would have used
join_primary before, we now use primary instead.
Primary
A healthy secondary node exists and has caught up with WAL replication. Specifically, the keeper reports
the primary state only when it has verified that the secondary is reported "sync" in
pg_stat_replication.sync_state, and with a WAL lag of 0.
The primary state is a strong assurance. It's the only state where we know we can fail over when
required.
During the transition from wait_primary to primary, the keeper also enables synchronous replication. This
means that after a failover the secondary will be fully up to date.
Wait_standby
Monitor decides this node is a standby. Node must wait until the primary has authorized it to connect and
setup hot standby replication.
Catchingup
The monitor assigns catchingup to the standby node when the primary is ready for a replication connection
(pg_hba.conf has been properly edited, connection role added, etc).
The standby node keeper runs pg_basebackup, connecting to the primary's hostname and port. The keeper
then edits recovery.conf and starts PostgreSQL in hot standby node.
Secondary
A node with this state is acting as a hot standby for the primary, and is up to date with the WAL log
there. In particular, it is within 16MB or 1 WAL segment of the primary.
Maintenance
The cluster administrator can manually move a secondary into the maintenance state to gracefully take it
offline. The primary will then transition from state primary to wait_primary, during which time the
secondary will be online to accept writes. When the old primary reaches the wait_primary state then the
secondary is safe to take offline with minimal consequences.
Prepare_maintenance
The cluster administrator can manually move a primary node into the maintenance state to gracefully take
it offline. The primary then transitions to the prepare_maintenance state to make sure the secondary is
not missing any writes. In the prepare_maintenance state, the primary shuts down.
Wait_maintenance
The custer administrator can manually move a secondary into the maintenance state to gracefully take it
offline. Before reaching the maintenance state though, we want to switch the primary node to asynchronous
replication, in order to avoid writes being blocked. In the state wait_maintenance the standby waits
until the primary has reached wait_primary.
Draining
A state between primary and demoted where replication buffers finish flushing. A draining node will not
accept new client writes, but will continue to send existing data to the secondary.
To implement that with Postgres we actually stop the service. When stopping, Postgres ensures that the
current replication buffers are flushed correctly to synchronous standbys.
Demoted
The primary keeper or its database were unresponsive past a certain threshold. The monitor assigns
demoted state to the primary to avoid a split-brain scenario where there might be two nodes that don't
communicate with each other and both accept client writes.
In that state the keeper stops PostgreSQL and prevents it from running.
Demote_timeout
If the monitor assigns the primary a demoted goal state but the primary keeper doesn't acknowledge
transitioning to that state within a timeout window, then the monitor assigns demote_timeout to the
primary.
Most commonly may happen when the primary machine goes silent. The keeper is not reporting to the
monitor.
Stop_replication
The stop_replication state is meant to ensure that the primary goes to the demoted state before the
standby goes to single and accepts writes (in case the primary can’t contact the monitor anymore). Before
promoting the secondary node, the keeper stops PostgreSQL on the primary to avoid split-brain situations.
For safety, when the primary fails to contact the monitor and fails to see the pg_auto_failover
connection in pg_stat_replication, then it goes to the demoted state of its own accord.
Prepare_promotion
The prepare_promotion state is meant to prepare the standby server to being promoted. This state allows
synchronisation on the monitor, making sure that the primary has stopped Postgres before promoting the
secondary, hence preventing split brain situations.
Report_LSN
The report_lsn state is assigned to standby nodes when a failover is orchestrated and there are several
standby nodes. In order to pick the furthest standby in the replication, pg_auto_failover first needs a
fresh report of the current LSN position reached on each standby node.
When a node reaches the report_lsn state, the replication stream is stopped, by restarting Postgres
without a primary_conninfo. This allows the primary node to detect Network Partitions, i.e. when the
primary can't connect to the monitor and there's no standby listed in pg_stat_replication.
Fast_forward
The fast_forward state is assigned to the selected promotion candidate during a failover when it won the
election thanks to the candidate priority settings, but the selected node is not the most advanced
standby node as reported in the report_lsn state.
Missing WAL bytes are fetched from one of the most advanced standby nodes by using Postgres cascading
replication features: it is possible to use any standby node in the primary_conninfo.
Dropped
The dropped state is assigned to a node when the pg_autoctl drop node command is used. This allows the
node to implement specific local actions before being entirely removed from the monitor database.
When a node reports reaching the dropped state, the monitor removes its entry. If a node is not reporting
anymore, maybe because it's completely unavailable, then it's possible to run the pg_autoctl drop node
--force command, and then the node entry is removed from the monitor.
pg_auto_failover keeper's State Machine
When built in TEST mode, it is then possible to use the following command to get a visual representation
of the Keeper's Finite State Machine:
$ PG_AUTOCTL_DEBUG=1 pg_autoctl do fsm gv | dot -Tsvg > fsm.svg
The dot program is part of the Graphviz suite and produces the following output:
[image: Keeper state machine] [image] Keeper State Machine.UNINDENT
FAILOVER AND FAULT TOLERANCE
At the heart of the pg_auto_failover implementation is a State Machine. The state machine is driven by
the monitor, and its transitions are implemented in the keeper service, which then reports success to the
monitor.
The keeper is allowed to retry transitions as many times as needed until they succeed, and reports also
failures to reach the assigned state to the monitor node. The monitor also implements frequent
health-checks targeting the registered PostgreSQL nodes.
When the monitor detects something is not as expected, it takes action by assigning a new goal state to
the keeper, that is responsible for implementing the transition to this new state, and then reporting.
Unhealthy Nodes
The pg_auto_failover monitor is responsible for running regular health-checks with every PostgreSQL node
it manages. A health-check is successful when it is able to connect to the PostgreSQL node using the
PostgreSQL protocol (libpq), imitating the pg_isready command.
How frequent those health checks are (5s by default), the PostgreSQL connection timeout in use (5s by
default), and how many times to retry in case of a failure before marking the node unhealthy (2 by
default) are GUC variables that you can set on the Monitor node itself. Remember, the monitor is
implemented as a PostgreSQL extension, so the setup is a set of PostgreSQL configuration settings:
SELECT name, setting
FROM pg_settings
WHERE name ~ 'pgautofailover\.health';
name | setting
-----------------------------------------+---------
pgautofailover.health_check_max_retries | 2
pgautofailover.health_check_period | 5000
pgautofailover.health_check_retry_delay | 2000
pgautofailover.health_check_timeout | 5000
(4 rows)
The pg_auto_failover keeper also reports if PostgreSQL is running as expected. This is useful for
situations where the PostgreSQL server / OS is running fine and the keeper (pg_autoctl run) is still
active, but PostgreSQL has failed. Situations might include File System is Full on the WAL disk, some
file system level corruption, missing files, etc.
Here's what happens to your PostgreSQL service in case of any single-node failure is observed:
• Primary node is monitored unhealthy
When the primary node is unhealthy, and only when the secondary node is itself in good health, then
the primary node is asked to transition to the DRAINING state, and the attached secondary is asked
to transition to the state PREPARE_PROMOTION. In this state, the secondary is asked to catch-up with
the WAL traffic from the primary, and then report success.
The monitor then continues orchestrating the promotion of the standby: it stops the primary
(implementing STONITH in order to prevent any data loss), and promotes the secondary into being a
primary now.
Depending on the exact situation that triggered the primary unhealthy, it's possible that the
secondary fails to catch-up with WAL from it, in that case after the
PREPARE_PROMOTION_CATCHUP_TIMEOUT the standby reports success anyway, and the failover sequence
continues from the monitor.
• Secondary node is monitored unhealthy
When the secondary node is unhealthy, the monitor assigns to it the state CATCHINGUP, and assigns
the state WAIT_PRIMARY to the primary node. When implementing the transition from PRIMARY to
WAIT_PRIMARY, the keeper disables synchronous replication.
When the keeper reports an acceptable WAL difference in the two nodes again, then the replication is
upgraded back to being synchronous. While a secondary node is not in the SECONDARY state, secondary
promotion is disabled.
• Monitor node has failed
Then the primary and secondary node just work as if you didn't have setup pg_auto_failover in the
first place, as the keeper fails to report local state from the nodes. Also, health checks are not
performed. It means that no automated failover may happen, even if needed.
Network Partitions
Adding to those simple situations, pg_auto_failover is also resilient to Network Partitions. Here's the
list of situation that have an impact to pg_auto_failover behavior, and the actions taken to ensure High
Availability of your PostgreSQL service:
• Primary can't connect to Monitor
Then it could be that either the primary is alone on its side of a network split, or that the
monitor has failed. The keeper decides depending on whether the secondary node is still connected to
the replication slot, and if we have a secondary, continues to serve PostgreSQL queries.
Otherwise, when the secondary isn't connected, and after the NETWORK_PARTITION_TIMEOUT has elapsed,
the primary considers it might be alone in a network partition: that's a potential split brain
situation and with only one way to prevent it. The primary stops, and reports a new state of
DEMOTE_TIMEOUT.
The network_partition_timeout can be setup in the keeper's configuration and defaults to 20s.
• Monitor can't connect to Primary
Once all the retries have been done and the timeouts are elapsed, then the primary node is
considered unhealthy, and the monitor begins the failover routine. This routine has several steps,
each of them allows to control our expectations and step back if needed.
For the failover to happen, the secondary node needs to be healthy and caught-up with the primary.
Only if we timeout while waiting for the WAL delta to resorb (30s by default) then the secondary can
be promoted with uncertainty about the data durability in the group.
• Monitor can't connect to Secondary
As soon as the secondary is considered unhealthy then the monitor changes the replication setting to
asynchronous on the primary, by assigning it the WAIT_PRIMARY state. Also the secondary is assigned
the state CATCHINGUP, which means it can't be promoted in case of primary failure.
As the monitor tracks the WAL delta between the two servers, and they both report it independently,
the standby is eligible to promotion again as soon as it's caught-up with the primary again, and at
this time it is assigned the SECONDARY state, and the replication will be switched back to
synchronous.
Failure handling and network partition detection
If a node cannot communicate to the monitor, either because the monitor is down or because there is a
problem with the network, it will simply remain in the same state until the monitor comes back.
If there is a network partition, it might be that the monitor and secondary can still communicate and the
monitor decides to promote the secondary since the primary is no longer responsive. Meanwhile, the
primary is still up-and-running on the other side of the network partition. If a primary cannot
communicate to the monitor it starts checking whether the secondary is still connected. In PostgreSQL,
the secondary connection automatically times out after 30 seconds. If last contact with the monitor and
the last time a connection from the secondary was observed are both more than 30 seconds in the past, the
primary concludes it is on the losing side of a network partition and shuts itself down. It may be that
the secondary and the monitor were actually down and the primary was the only node that was alive, but we
currently do not have a way to distinguish such a situation. As with consensus algorithms, availability
can only be correctly preserved if at least 2 out of 3 nodes are up.
In asymmetric network partitions, the primary might still be able to talk to the secondary, while unable
to talk to the monitor. During failover, the monitor therefore assigns the secondary the stop_replication
state, which will cause it to disconnect from the primary. After that, the primary is expected to shut
down after at least 30 and at most 60 seconds. To factor in worst-case scenarios, the monitor waits for
90 seconds before promoting the secondary to become the new primary.
SECURITY SETTINGS FOR PG_AUTO_FAILOVER
In order to be able to orchestrate fully automated failovers, pg_auto_failover needs to be able to
establish the following Postgres connections:
• from the monitor node to each Postgres node to check the node's “health”
• from each Postgres node to the monitor to implement our node_active protocol and fetch the current
assigned state for this node
• from the secondary node to the primary node for Postgres streaming replication.
Postgres Client authentication is controlled by a configuration file: pg_hba.conf. This file contains a
list of rules where each rule may allow or reject a connection attempt.
For pg_auto_failover to work as intended, some HBA rules need to be added to each node configuration. You
can choose to provision the pg_hba.conf file yourself thanks to pg_autoctl options' --skip-pg-hba, or you
can use the following options to control which kind of rules are going to be added for you.
Postgres HBA rules
For your application to be able to connect to the current Postgres primary servers, some application
specific HBA rules have to be added to pg_hba.conf. There is no provision for doing that in
pg_auto_failover.
In other words, it is expected that you have to edit pg_hba.conf to open connections for your application
needs.
The trust security model
As its name suggests the trust security model is not enabling any kind of security validation. This
setting is popular for testing deployments though, as it makes it very easy to verify that everything
works as intended before putting security restrictions in place.
To enable a “trust” security model with pg_auto_failover, use the pg_autoctl option --auth trust when
creating nodes:
$ pg_autoctl create monitor --auth trust ...
$ pg_autoctl create postgres --auth trust ...
$ pg_autoctl create postgres --auth trust ...
When using --auth trust pg_autoctl adds new HBA rules in the monitor and the Postgres nodes to enable
connections as seen above.
Authentication with passwords
To setup pg_auto_failover with password for connections, you can use one of the password based
authentication methods supported by Postgres, such as password or scram-sha-256. We recommend the latter,
as in the following example:
$ pg_autoctl create monitor --auth scram-sha-256 ...
The pg_autoctl does not set the password for you. The first step is to set the database user password in
the monitor database thanks to the following command:
$ psql postgres://monitor.host/pg_auto_failover
> alter user autoctl_node password 'h4ckm3';
Now that the monitor is ready with our password set for the autoctl_node user, we can use the password in
the monitor connection string used when creating Postgres nodes.
On the primary node, we can create the Postgres setup as usual, and then set our replication password,
that we will use if we are demoted and then re-join as a standby:
$ pg_autoctl create postgres \
--auth scram-sha-256 \
... \
--monitor postgres://autoctl_node:h4ckm3@monitor.host/pg_auto_failover
$ pg_autoctl config set replication.password h4ckm3m0r3
The second Postgres node is going to be initialized as a secondary and pg_autoctl then calls
pg_basebackup at create time. We need to have the replication password already set at this time, and we
can achieve that the following way:
$ export PGPASSWORD=h4ckm3m0r3
$ pg_autoctl create postgres \
--auth scram-sha-256 \
... \
--monitor postgres://autoctl_node:h4ckm3@monitor.host/pg_auto_failover
$ pg_autoctl config set replication.password h4ckm3m0r3
Note that you can use The Password File mechanism as discussed in the Postgres documentation in order to
maintain your passwords in a separate file, not in your main pg_auto_failover configuration file. This
also avoids using passwords in the environment and in command lines.
Encryption of network communications
Postgres knows how to use SSL to enable network encryption of all communications, including
authentication with passwords and the whole data set when streaming replication is used.
To enable SSL on the server an SSL certificate is needed. It could be as simple as a self-signed
certificate, and pg_autoctl creates such a certificate for you when using --ssl-self-signed command line
option:
$ pg_autoctl create monitor --ssl-self-signed ... \
--auth scram-sha-256 ... \
--ssl-mode require \
...
$ pg_autoctl create postgres --ssl-self-signed ... \
--auth scram-sha-256 ... \
...
$ pg_autoctl create postgres --ssl-self-signed ... \
--auth scram-sha-256 ... \
...
In that example we setup SSL connections to encrypt the network traffic, and we still have to setup an
authentication mechanism exactly as in the previous sections of this document. Here scram-sha-256 has
been selected, and the password will be sent over an encrypted channel.
When using the --ssl-self-signed option, pg_autoctl creates a self-signed certificate, as per the
Postgres documentation at the Creating Certificates page.
The certificate subject CN defaults to the --hostname parameter, which can be given explicitly or
computed by pg_autoctl as either your hostname when you have proper DNS resolution, or your current IP
address.
Self-signed certificates provide protection against eavesdropping; this setup does NOT protect against
Man-In-The-Middle attacks nor Impersonation attacks. See PostgreSQL documentation page SSL Support for
details.
Using your own SSL certificates
In many cases you will want to install certificates provided by your local security department and signed
by a trusted Certificate Authority. In that case one solution is to use --skip-pg-hba and do the whole
setup yourself.
It is still possible to give the certificates to pg_auto_failover and have it handle the Postgres setup
for you:
$ pg_autoctl create monitor --ssl-ca-file root.crt \
--ssl-crl-file root.crl \
--server-cert server.crt \
--server-key server.key \
--ssl-mode verify-full \
...
$ pg_autoctl create postgres --ssl-ca-file root.crt \
--server-cert server.crt \
--server-key server.key \
--ssl-mode verify-full \
...
$ pg_autoctl create postgres --ssl-ca-file root.crt \
--server-cert server.crt \
--server-key server.key \
--ssl-mode verify-full \
...
The option --ssl-mode can be used to force connection strings used by pg_autoctl to contain your
preferred ssl mode. It defaults to require when using --ssl-self-signed and to allow when --no-ssl is
used. Here, we set --ssl-mode to verify-full which requires SSL Certificates Authentication, covered
next.
The default --ssl-mode when providing your own certificates (signed by your trusted CA) is then
verify-full. This setup applies to the client connection where the server identity is going to be checked
against the root certificate provided with --ssl-ca-file and the revocation list optionally provided with
the --ssl-crl-file. Both those files are used as the respective parameters sslrootcert and sslcrl in
pg_autoctl connection strings to both the monitor and the streaming replication primary server.
SSL Certificates Authentication
Given those files, it is then possible to use certificate based authentication of client connections. For
that, it is necessary to prepare client certificates signed by your root certificate private key and
using the target user name as its CN, as per Postgres documentation for Certificate Authentication:
The cn (Common Name) attribute of the certificate will be compared to the requested database user
name, and if they match the login will be allowed
For enabling the cert authentication method with pg_auto_failover, you need to prepare a Client
Certificate for the user postgres and used by pg_autoctl when connecting to the monitor, to place in
~/.postgresql/postgresql.crt along with its key ~/.postgresql/postgresql.key, in the home directory of
the user that runs the pg_autoctl service (which defaults to postgres).
Then you need to create a user name map as documented in Postgres page User Name Maps so that your
certificate can be used to authenticate pg_autoctl users.
The ident map in pg_ident.conf on the pg_auto_failover monitor should then have the following entry, to
allow postgres to connect as the autoctl_node user for pg_autoctl operations:
# MAPNAME SYSTEM-USERNAME PG-USERNAME
# pg_autoctl runs as postgres and connects to the monitor autoctl_node user
pgautofailover postgres autoctl_node
To enable streaming replication, the pg_ident.conf file on each Postgres node should now allow the
postgres user in the client certificate to connect as the pgautofailover_replicator database user:
# MAPNAME SYSTEM-USERNAME PG-USERNAME
# pg_autoctl runs as postgres and connects to the monitor autoctl_node user
pgautofailover postgres pgautofailover_replicator
Given that user name map, you can then use the cert authentication method. As with the pg_ident.conf
provisioning, it is best to now provision the HBA rules yourself, using the --skip-pg-hba option:
$ pg_autoctl create postgres --skip-pg-hba --ssl-ca-file ...
The HBA rule will use the authentication method cert with a map option, and might then look like the
following on the monitor:
# allow certificate based authentication to the monitor
hostssl pg_auto_failover autoctl_node 10.0.0.0/8 cert map=pgautofailover
Then your pg_auto_failover nodes on the 10.0.0.0 network are allowed to connect to the monitor with the
user autoctl_node used by pg_autoctl, assuming they have a valid and trusted client certificate.
The HBA rule to use on the Postgres nodes to allow for Postgres streaming replication connections looks
like the following:
# allow streaming replication for pg_auto_failover nodes
hostssl replication pgautofailover_replicator 10.0.0.0/8 cert map=pgautofailover
Because the Postgres server runs as the postgres system user, the connection to the primary node can be
made with SSL enabled and will then use the client certificates installed in the postgres home directory
in ~/.postgresql/postgresql.{key,cert} locations.
Postgres HBA provisioning
While pg_auto_failover knows how to manage the Postgres HBA rules that are necessary for your stream
replication needs and for its monitor protocol, it will not manage the Postgres HBA rules that are needed
for your applications.
If you have your own HBA provisioning solution, you can include the rules needed for pg_auto_failover and
then use the --skip-pg-hba option to the pg_autoctl create commands.
Enable SSL connections on an existing setup
Whether you upgrade pg_auto_failover from a previous version that did not have support for the SSL
features, or when you started with --no-ssl and later change your mind, it is possible with
pg_auto_failover to add SSL settings on system that has already been setup without explicit SSL support.
In this section we detail how to upgrade to SSL settings.
Installing Self-Signed certificates on-top of an already existing pg_auto_failover setup is done with one
of the following pg_autoctl command variants, depending if you want self-signed certificates or fully
verified ssl certificates:
$ pg_autoctl enable ssl --ssl-self-signed --ssl-mode required
$ pg_autoctl enable ssl --ssl-ca-file root.crt \
--ssl-crl-file root.crl \
--server-cert server.crt \
--server-key server.key \
--ssl-mode verify-full
The pg_autoctl enable ssl command edits the postgresql-auto-failover.conf Postgres configuration file to
match the command line arguments given and enable SSL as instructed, and then updates the pg_autoctl
configuration.
The connection string to connect to the monitor is also automatically updated by the pg_autoctl enable
ssl command. You can verify your new configuration with:
$ pg_autoctl config get pg_autoctl.monitor
Note that an already running pg_autoctl daemon will try to reload its configuration after pg_autoctl
enable ssl has finished. In some cases this is not possible to do without a restart. So be sure to check
the logs from a running daemon to confirm that the reload succeeded. If it did not you may need to
restart the daemon to ensure the new connection string is used.
The HBA settings are not edited, irrespective of the --skip-pg-hba that has been used at creation time.
That's because the host records match either SSL or non-SSL connection attempts in Postgres HBA file, so
the pre-existing setup will continue to work. To enhance the SSL setup, you can manually edit the HBA
files and change the existing lines from host to hostssl to disallow unencrypted connections at the
server side.
In summary, to upgrade an existing pg_auto_failover setup to enable SSL:
1. run the pg_autoctl enable ssl command on your monitor and then all the Postgres nodes,
2. on the Postgres nodes, review your pg_autoctl logs to make sure that the reload operation has been
effective, and review your Postgres settings to verify that you have the expected result,
3. review your HBA rules setup to change the pg_auto_failover rules from host to hostssl to disallow
insecure connections.
CITUS SUPPORT
The usual pg_autoctl commands work both with Postgres standalone nodes and with Citus nodes.
[image: pg_auto_failover architecture with a Citus formation] [image] pg_auto_failover architecture
with a Citus formation.UNINDENT
When using pg_auto_failover with Citus, a pg_auto_failover formation is composed of a coordinator and a
set of worker nodes.
When High-Availability is enabled at the formation level, which is the default, then a minimum of two
coordinator nodes are required: a primary and a secondary coordinator to be able to orchestrate a
failover when needed.
The same applies to the worker nodes: when using pg_auto_failover for Citus HA, then each worker node
is a pg_auto_failover group in the formation, and each worker group is setup with at least two nodes
(primary, secondary).
Setting-up your first Citus formation
Have a look at our documentation of Citus Tutorial for more details with a full tutorial setup on a
single VM, for testing and QA.
Citus specific commands and operations
When setting up Citus with pg_auto_failover, the following Citus specific commands are provided. Other
pg_autoctl commands work as usual when deploying a Citus formation, so that you can use the rest of this
documentation to operate your Citus deployments.
pg_autoctl create coordinator
This creates a Citus coordinator, that is to say a Postgres node with the Citus extension loaded and
ready to act as a coordinator. The coordinator is always places in the pg_auto_failover group zero of a
given formation.
See pg_autoctl create coordinator for details.
IMPORTANT:
The default --dbname is the same as the current system user name, which in many case is going to be
postgres. Please make sure to use the --dbname option with the actual database that you're going to
use with your application.
Citus does not support multiple databases, you have to use the database where Citus is created. When
using Citus, that is essential to the well behaving of worker failover.
pg_autoctl create worker
This command creates a new Citus worker node, that is to say a Postgres node with the Citus extensions
loaded, and registered to the Citus coordinator created with the previous command. Because the Citus
coordinator is always given group zero, the pg_auto_failover monitor knows how to reach the Citus
coordinator and automate workers registration.
The default worker creation policy is to assign the primary role to the first worker registered, then
secondary in the same group, then primary in a new group, etc.
If you want to extend an existing group to have a third worker node in the same group, enabling
multiple-standby capabilities in your setup, then make sure to use the --group option to the pg_autoctl
create worker command.
See pg_autoctl create worker for details.
pg_autoctl activate
This command calls the Citus “activation” API so that a node can be used to host shards for your
reference and distributed tables.
When creating a Citus worker, pg_autoctl create worker automatically activates the worker node to the
coordinator. You only need this command when something unexpected have happened and you want to manually
make sure the worker node has been activated at the Citus coordinator level.
Starting with Citus 10 it is also possible to activate the coordinator itself as a node with shard
placement. Use pg_autoctl activate on your Citus coordinator node manually to use that feature.
When the Citus coordinator is activated, an extra step is then needed for it to host shards of
distributed tables. If you want your coordinator to have shards, then have a look at the Citus API
citus_set_node_property to set the shouldhaveshards property to true.
See pg_autoctl activate for details.
Citus worker failover
When a failover is orchestrated by pg_auto_failover for a Citus worker node, Citus offers the opportunity
to make the failover close to transparent to the application. Because the application connects to the
coordinator, which in turn connects to the worker nodes, then it is possible with Citus to _pause_ the
SQL write traffic on the coordinator for the shards hosted on a failed worker node. The Postgres failover
then happens while the traffic is kept on the coordinator, and resumes as soon as a secondary worker node
is ready to accept read-write queries.
This is implemented thanks to Citus smart locking strategy in its citus_update_node API, and
pg_auto_failover takes full benefit with a special built set of FSM transitions for Citus workers.
Citus Secondaries and read-replica
It is possible to setup Citus read-only replicas. This Citus feature allows using a set of dedicated
nodes (both coordinator and workers) to serve read-only traffic, such as reporting, analytics, or other
parts of your workload that are read-only.
Citus read-replica nodes are a solution for load-balancing. Those nodes can't be used as HA failover
targets, and thus have their candidate-priority set to zero. This setting of a read-replica can not be
changed later.
This setup is done by setting the Citus property citus.use_secondary_nodes to always (it defaults to
never), and the Citus property citus.cluster_name to your read-only cluster name.
Both of those settings are entirely supported and managed by pg_autoctl when using the --citus-secondary
--cluster-name cluster_d options to the pg_autoctl create coordinator|worker commands.
Here is an example where we have created a formation with three nodes for HA for the coordinator (one
primary and two secondary nodes), then a single worker node with the same three nodes setup for HA, and
then one read-replica environment on-top of that, for a total of 8 nodes:
$ pg_autoctl show state
Name | Node | Host:Port | LSN | Reachable | Current State | Assigned State
---------+-------+----------------+-----------+-----------+---------------------+--------------------
coord0a | 0/1 | localhost:5501 | 0/5003298 | yes | primary | primary
coord0b | 0/3 | localhost:5502 | 0/5003298 | yes | secondary | secondary
coord0c | 0/6 | localhost:5503 | 0/5003298 | yes | secondary | secondary
coord0d | 0/7 | localhost:5504 | 0/5003298 | yes | secondary | secondary
worker1a | 1/2 | localhost:5505 | 0/4000170 | yes | primary | primary
worker1b | 1/4 | localhost:5506 | 0/4000170 | yes | secondary | secondary
worker1c | 1/5 | localhost:5507 | 0/4000170 | yes | secondary | secondary
reader1d | 1/8 | localhost:5508 | 0/4000170 | yes | secondary | secondary
Nodes named coord0d and reader1d are members of the read-replica cluster cluster_d. We can see that a
read-replica cluster needs a dedicated coordinator and then one dedicated worker node per group.
TIP:
It is possible to name the nodes in a pg_auto_failover formation either at creation time or later,
using one of those commands:
$ pg_autoctl create worker --name ...
$ pg_autoctl set node metadata --name ...
Here coord0d is the node name for the dedicated coordinator for cluster_d, and reader1d is the node
name for the dedicated worker for cluster_d in the worker group 1 (the only worker group in that
setup).
Now the usual command to show the connection strings for your application is listing the read-replica
setup that way:
$ pg_autoctl show uri
Type | Name | Connection String
-------------+-----------+-------------------------------
monitor | monitor | postgres://autoctl_node@localhost:5500/pg_auto_failover?sslmode=prefer
formation | default | postgres://localhost:5503,localhost:5501,localhost:5502/postgres?target_session_attrs=read-write&sslmode=prefer
read-replica | cluster_d | postgres://localhost:5504/postgres?sslmode=prefer
Given that setup, your application can now use the formation default Postgres URI to connect to the
highly-available read-write service, or to the read-replica cluster_d service to connect to the read-only
replica where you can offload some of your SQL workload.
When connecting to the cluster_d connection string, the Citus properties citus.use_secondary_nodes and
citus.cluster_name are automatically setup to their expected values, of course.
CITUS TUTORIAL
In this guide we’ll create a Citus cluster with a coordinator node and three workers. Every node will
have a secondary for failover. We’ll simulate failure in the coordinator and worker nodes and see how the
system continues to function.
This tutorial uses docker-compose in order to separate the architecture design from some of the
implementation details. This allows reasoning at the architecture level within this tutorial, and better
see which software component needs to be deployed and run on which node.
The setup provided in this tutorial is good for replaying at home in the lab. It is not intended to be
production ready though. In particular, no attention have been spent on volume management. After all,
this is a tutorial: the goal is to walk through the first steps of using pg_auto_failover to provide HA
to a Citus formation.
Pre-requisites
When using docker-compose we describe a list of services, each service may run on one or more nodes, and
each service just runs a single isolated process in a container.
Within the context of a tutorial, or even a development environment, this matches very well to
provisioning separate physical machines on-prem, or Virtual Machines either on-prem on in a Cloud
service.
The docker image used in this tutorial is named pg_auto_failover:citus. It can be built locally when
using the attached Dockerfile found within the GitHub repository for pg_auto_failover.
To build the image, either use the provided Makefile and run make build, or run the docker build command
directly:
$ git clone https://github.com/citusdata/pg_auto_failover
$ cd pg_auto_failover/docs/cluster
$ docker build -t pg_auto_failover:citus -f Dockerfile ../..
$ docker-compose build
Our first Citus Cluster
To create a cluster we use the following docker-compose definition:
version: "3.9" # optional since v1.27.0
services:
monitor:
image: pg_auto_failover:citus
environment:
PGDATA: /tmp/pgaf
command: |
pg_autoctl create monitor --ssl-self-signed --auth trust --run
expose:
- 5432
coord:
image: pg_auto_failover:citus
environment:
PGDATA: /tmp/pgaf
PGUSER: citus
PGDATABASE: citus
PG_AUTOCTL_MONITOR: "postgresql://autoctl_node@monitor/pg_auto_failover"
expose:
- 5432
command: |
pg_autoctl create coordinator --ssl-self-signed --auth trust --pg-hba-lan --run
worker:
image: pg_auto_failover:citus
environment:
PGDATA: /tmp/pgaf
PGUSER: citus
PGDATABASE: citus
PG_AUTOCTL_MONITOR: "postgresql://autoctl_node@monitor/pg_auto_failover"
expose:
- 5432
command: |
pg_autoctl create worker --ssl-self-signed --auth trust --pg-hba-lan --run
To run the full Citus cluster with HA from this definition, we can use the following command:
$ docker-compose up --scale coord=2 --scale worker=6
The command above starts the services up. The command also specifies a --scale option that is different
for each service. We need:
• one monitor node, and the default scale for a service is 1,
• one primary Citus coordinator node and one secondary Cituscoordinator node, which is to say two
coordinator nodes,
• and three Citus worker nodes, each worker with both a primary Postgres node and a secondary Postgres
node, so that's a scale of 6 here.
The default policy for the pg_auto_failover monitor is to assign a primary and a secondary per auto
failover Group. In our case, every node being provisioned with the same command, we benefit from that
default policy:
$ pg_autoctl create worker --ssl-self-signed --auth trust --pg-hba-lan --run
When provisioning a production cluster, it is often required to have a better control over which node
participates in which group, then using the --group N option in the pg_autoctl create worker command
line.
Within a given group, the first node that registers is a primary, and the other nodes are secondary
nodes. The monitor takes care of that in a way that we don't have to. In a High Availability setup, every
node should be ready to be promoted primary at any time, so knowing which node in a group is assigned
primary first is not very interesting.
While the cluster is being provisionned by docker-compose, you can run the following command and have a
dynamic dashboard to follow what's happening. The following command is like top for pg_auto_failover:
$ docker-compose exec monitor pg_autoctl watch
Because the pg_basebackup operation that is used to create the secondary nodes takes some time when using
Citus, because of the first CHECKPOINT which is quite slow. So at first when inquiring about the cluster
state you might see the following output:
$ docker-compose exec monitor pg_autoctl show state
Name | Node | Host:Port | TLI: LSN | Connection | Reported State | Assigned State
---------+-------+-------------------+----------------+--------------+---------------------+--------------------
coord0a | 0/1 | cd52db444544:5432 | 1: 0/200C4A0 | read-write | wait_primary | wait_primary
coord0b | 0/2 | 66a31034f2e4:5432 | 1: 0/0 | none ! | wait_standby | catchingup
worker1a | 1/3 | dae7c062e2c1:5432 | 1: 0/2003B18 | read-write | wait_primary | wait_primary
worker1b | 1/4 | 397e6069b09b:5432 | 1: 0/0 | none ! | wait_standby | catchingup
worker2a | 2/5 | 5bf86f9ef784:5432 | 1: 0/2006AB0 | read-write | wait_primary | wait_primary
worker2b | 2/6 | 23498b801a61:5432 | 1: 0/0 | none ! | wait_standby | catchingup
worker3a | 3/7 | c23610380024:5432 | 1: 0/2003B18 | read-write | wait_primary | wait_primary
worker3b | 3/8 | 2ea8aac8a04a:5432 | 1: 0/0 | none ! | wait_standby | catchingup
After a while though (typically around a minute or less), you can run that same command again for stable
result:
$ docker-compose exec monitor pg_autoctl show state
Name | Node | Host:Port | TLI: LSN | Connection | Reported State | Assigned State
---------+-------+-------------------+----------------+--------------+---------------------+--------------------
coord0a | 0/1 | cd52db444544:5432 | 1: 0/3127AD0 | read-write | primary | primary
coord0b | 0/2 | 66a31034f2e4:5432 | 1: 0/3127AD0 | read-only | secondary | secondary
worker1a | 1/3 | dae7c062e2c1:5432 | 1: 0/311B610 | read-write | primary | primary
worker1b | 1/4 | 397e6069b09b:5432 | 1: 0/311B610 | read-only | secondary | secondary
worker2a | 2/5 | 5bf86f9ef784:5432 | 1: 0/311B610 | read-write | primary | primary
worker2b | 2/6 | 23498b801a61:5432 | 1: 0/311B610 | read-only | secondary | secondary
worker3a | 3/7 | c23610380024:5432 | 1: 0/311B648 | read-write | primary | primary
worker3b | 3/8 | 2ea8aac8a04a:5432 | 1: 0/311B648 | read-only | secondary | secondary
You can see from the above that the coordinator node has a primary and secondary instance for high
availability. When connecting to the coordinator, clients should try connecting to whichever instance is
running and supports reads and writes.
We can review the available Postgres URIs with the pg_autoctl show uri command:
$ docker-compose exec monitor pg_autoctl show uri
Type | Name | Connection String
-------------+---------+-------------------------------
monitor | monitor | postgres://autoctl_node@552dd89d5d63:5432/pg_auto_failover?sslmode=require
formation | default | postgres://66a31034f2e4:5432,cd52db444544:5432/citus?target_session_attrs=read-write&sslmode=require
To check that Citus worker nodes have been registered to the coordinator, we can run a psql session right
from the coordinator container:
$ docker-compose exec coord psql -d citus -c 'select * from citus_get_active_worker_nodes();'
node_name | node_port
--------------+-----------
dae7c062e2c1 | 5432
5bf86f9ef784 | 5432
c23610380024 | 5432
(3 rows)
We are now reaching the limits of using a simplified docker-compose setup. When using the --scale
option, it is not possible to give a specific hostname to each running node, and then we get a randomly
generated string instead or useful node names such as worker1a or worker3b.
Create a Citus Cluster, take two
In order to implement the following architecture, we need to introduce a more complex docker-compose file
than in the previous section.
[image: pg_auto_failover architecture with a Citus formation] [image] pg_auto_failover architecture
with a Citus formation.UNINDENT
This time we create a cluster using the following docker-compose definition:
version: "3.9" # optional since v1.27.0
x-coord: &coordinator
image: pg_auto_failover:citus
environment:
PGDATA: /tmp/pgaf
PGUSER: citus
PGDATABASE: citus
PG_AUTOCTL_HBA_LAN: true
PG_AUTOCTL_AUTH_METHOD: "trust"
PG_AUTOCTL_SSL_SELF_SIGNED: true
PG_AUTOCTL_MONITOR: "postgresql://autoctl_node@monitor/pg_auto_failover"
expose:
- 5432
x-worker: &worker
image: pg_auto_failover:citus
environment:
PGDATA: /tmp/pgaf
PGUSER: citus
PGDATABASE: citus
PG_AUTOCTL_HBA_LAN: true
PG_AUTOCTL_AUTH_METHOD: "trust"
PG_AUTOCTL_SSL_SELF_SIGNED: true
PG_AUTOCTL_MONITOR: "postgresql://autoctl_node@monitor/pg_auto_failover"
expose:
- 5432
services:
app:
build:
context: .
dockerfile: Dockerfile.app
environment:
PGUSER: citus
PGDATABASE: citus
PGHOST: coord0a,coord0b
PGPORT: 5432
PGAPPNAME: demo
PGSSLMODE: require
PGTARGETSESSIONATTRS: read-write
monitor:
image: pg_auto_failover:citus
environment:
PGDATA: /tmp/pgaf
PG_AUTOCTL_SSL_SELF_SIGNED: true
expose:
- 5432
command: |
pg_autoctl create monitor --auth trust --run
coord0a:
<<: *coordinator
hostname: coord0a
command: |
pg_autoctl create coordinator --name coord0a --run
coord0b:
<<: *coordinator
hostname: coord0b
command: |
pg_autoctl create coordinator --name coord0b --run
worker1a:
<<: *worker
hostname: worker1a
command: |
pg_autoctl create worker --group 1 --name worker1a --run
worker1b:
<<: *worker
hostname: worker1b
command: |
pg_autoctl create worker --group 1 --name worker1b --run
worker2a:
<<: *worker
hostname: worker2a
command: |
pg_autoctl create worker --group 2 --name worker2a --run
worker2b:
<<: *worker
hostname: worker2b
command: |
pg_autoctl create worker --group 2 --name worker2b --run
worker3a:
<<: *worker
hostname: worker3a
command: |
pg_autoctl create worker --group 3 --name worker3a --run
worker3b:
<<: *worker
hostname: worker3b
command: |
pg_autoctl create worker --group 3 --name worker3b --run
This definition is a little more involved than the previous one. We take benefit from YAML anchors and
aliases to define a template for our coordinator nodes and worker nodes, and then apply that template to
the actual nodes.
Also this time we provision an application service (named "app") that sits in the background and allow us
to later connect to our current primary coordinator. See Dockerfile.app for the complete definition of
this service.
We start this cluster with a simplified command line this time:
$ docker-compose up
And this time we get the following cluster as a result:
$ docker-compose exec monitor pg_autoctl show state
Name | Node | Host:Port | TLI: LSN | Connection | Reported State | Assigned State
---------+-------+---------------+----------------+--------------+---------------------+--------------------
coord0a | 0/3 | coord0a:5432 | 1: 0/312B040 | read-write | primary | primary
coord0b | 0/4 | coord0b:5432 | 1: 0/312B040 | read-only | secondary | secondary
worker1a | 1/1 | worker1a:5432 | 1: 0/311C550 | read-write | primary | primary
worker1b | 1/2 | worker1b:5432 | 1: 0/311C550 | read-only | secondary | secondary
worker2b | 2/7 | worker2b:5432 | 2: 0/5032698 | read-write | primary | primary
worker2a | 2/8 | worker2a:5432 | 2: 0/5032698 | read-only | secondary | secondary
worker3a | 3/5 | worker3a:5432 | 1: 0/311C870 | read-write | primary | primary
worker3b | 3/6 | worker3b:5432 | 1: 0/311C870 | read-only | secondary | secondary
And then we have the following application connection string to use:
$ docker-compose exec monitor pg_autoctl show uri
Type | Name | Connection String
-------------+---------+-------------------------------
monitor | monitor | postgres://autoctl_node@f0135b83edcd:5432/pg_auto_failover?sslmode=require
formation | default | postgres://coord0b:5432,coord0a:5432/citus?target_session_attrs=read-write&sslmode=require
And finally, the nodes being registered as Citus worker nodes also make more sense:
$ docker-compose exec coord0a psql -d citus -c 'select * from citus_get_active_worker_nodes()'
node_name | node_port
-----------+-----------
worker1a | 5432
worker3a | 5432
worker2b | 5432
(3 rows)
IMPORTANT:
At this point, it is important to note that the Citus coordinator only knows about the primary nodes
in each group. The High Availability mechanisms are all implemented in pg_auto_failover, which mostly
uses the Citus API citus_update_node during worker node failovers.
Our first Citus worker failover
We see that in the citus_get_active_worker_nodes() output we have worker1a, worker2b, and worker3a. As
mentioned before, that should have no impact on the operations of the Citus cluster when nodes are all
dimensionned the same.
That said, some readers among you will prefer to have the A nodes as primaries to get started with. So
let's implement our first worker failover then. With pg_auto_failover, this is as easy as doing:
$ docker-compose exec monitor pg_autoctl perform failover --group 2
15:40:03 9246 INFO Waiting 60 secs for a notification with state "primary" in formation "default" and group 2
15:40:03 9246 INFO Listening monitor notifications about state changes in formation "default" and group 2
15:40:03 9246 INFO Following table displays times when notifications are received
Time | Name | Node | Host:Port | Current State | Assigned State
---------+----------+-------+---------------+---------------------+--------------------
22:58:42 | worker2b | 2/7 | worker2b:5432 | primary | draining
22:58:42 | worker2a | 2/8 | worker2a:5432 | secondary | prepare_promotion
22:58:42 | worker2a | 2/8 | worker2a:5432 | prepare_promotion | prepare_promotion
22:58:42 | worker2a | 2/8 | worker2a:5432 | prepare_promotion | wait_primary
22:58:42 | worker2b | 2/7 | worker2b:5432 | primary | demoted
22:58:42 | worker2b | 2/7 | worker2b:5432 | draining | demoted
22:58:42 | worker2b | 2/7 | worker2b:5432 | demoted | demoted
22:58:43 | worker2a | 2/8 | worker2a:5432 | wait_primary | wait_primary
22:58:44 | worker2b | 2/7 | worker2b:5432 | demoted | catchingup
22:58:46 | worker2b | 2/7 | worker2b:5432 | catchingup | catchingup
22:58:46 | worker2b | 2/7 | worker2b:5432 | catchingup | secondary
22:58:46 | worker2b | 2/7 | worker2b:5432 | secondary | secondary
22:58:46 | worker2a | 2/8 | worker2a:5432 | wait_primary | primary
22:58:46 | worker2a | 2/8 | worker2a:5432 | primary | primary
So it took around 5 seconds to do a full worker failover in worker group 2. Now we'll do the same on the
group 1 to fix the other situation, and review the resulting cluster state.
$ docker-compose exec monitor pg_autoctl show state
Name | Node | Host:Port | TLI: LSN | Connection | Reported State | Assigned State
---------+-------+---------------+----------------+--------------+---------------------+--------------------
coord0a | 0/3 | coord0a:5432 | 1: 0/312ADA8 | read-write | primary | primary
coord0b | 0/4 | coord0b:5432 | 1: 0/312ADA8 | read-only | secondary | secondary
worker1a | 1/1 | worker1a:5432 | 1: 0/311B610 | read-write | primary | primary
worker1b | 1/2 | worker1b:5432 | 1: 0/311B610 | read-only | secondary | secondary
worker2b | 2/7 | worker2b:5432 | 2: 0/50000D8 | read-only | secondary | secondary
worker2a | 2/8 | worker2a:5432 | 2: 0/50000D8 | read-write | primary | primary
worker3a | 3/5 | worker3a:5432 | 1: 0/311B648 | read-write | primary | primary
worker3b | 3/6 | worker3b:5432 | 1: 0/311B648 | read-only | secondary | secondary
Which seen from the Citus coordinator, looks like the following:
$ docker-compose exec coord0a psql -d citus -c 'select * from citus_get_active_worker_nodes()'
node_name | node_port
-----------+-----------
worker1a | 5432
worker3a | 5432
worker2a | 5432
(3 rows)
Distribute Data to Workers
Let's create a database schema with a single distributed table.
$ docker-compose exec app psql
-- in psql
CREATE TABLE companies
(
id bigserial PRIMARY KEY,
name text NOT NULL,
image_url text,
created_at timestamp without time zone NOT NULL,
updated_at timestamp without time zone NOT NULL
);
SELECT create_distributed_table('companies', 'id');
Next download and ingest some sample data, still from within our psql session:
\copy companies from program 'curl -o- https://examples.citusdata.com/mt_ref_arch/companies.csv' with csv
# ( COPY 75 )
Handle Worker Failure
Now we'll intentionally crash a worker's primary node and observe how the pg_auto_failover monitor
unregisters that node in the coordinator and registers the secondary instead.
# the pg_auto_failover keeper process will be unable to resurrect
# the worker node if pg_control has been removed
$ docker-compose exec worker1a rm /tmp/pgaf/global/pg_control
# shut it down
$ docker-compose exec worker1a /usr/lib/postgresql/14/bin/pg_ctl stop -D /tmp/pgaf
The keeper will attempt to start worker 1a three times and then report the failure to the monitor, who
promotes worker1b to replace worker1a. Citus worker worker1a is unregistered with the coordinator node,
and worker1b is registered in its stead.
Asking the coordinator for active worker nodes now shows worker1b, worker2a, and worker3a:
$ docker-compose exec app psql -c 'select * from master_get_active_worker_nodes();'
node_name | node_port
-----------+-----------
worker3a | 5432
worker2a | 5432
worker1b | 5432
(3 rows)
Finally, verify that all rows of data are still present:
$ docker-compose exec app psql -c 'select count(*) from companies;'
count
-------
75
Meanwhile, the keeper on worker 1a heals the node. It runs pg_basebackup to fetch the current PGDATA from
worker1a. This restores, among other things, a new copy of the file we removed. After streaming
replication completes, worker1b becomes a full-fledged primary and worker1a its secondary.
$ docker-compose exec monitor pg_autoctl show state
Name | Node | Host:Port | TLI: LSN | Connection | Reported State | Assigned State
---------+-------+---------------+----------------+--------------+---------------------+--------------------
coord0a | 0/3 | coord0a:5432 | 1: 0/3178B20 | read-write | primary | primary
coord0b | 0/4 | coord0b:5432 | 1: 0/3178B20 | read-only | secondary | secondary
worker1a | 1/1 | worker1a:5432 | 2: 0/504C400 | read-only | secondary | secondary
worker1b | 1/2 | worker1b:5432 | 2: 0/504C400 | read-write | primary | primary
worker2b | 2/7 | worker2b:5432 | 2: 0/50FF048 | read-only | secondary | secondary
worker2a | 2/8 | worker2a:5432 | 2: 0/50FF048 | read-write | primary | primary
worker3a | 3/5 | worker3a:5432 | 1: 0/31CD8C0 | read-write | primary | primary
worker3b | 3/6 | worker3b:5432 | 1: 0/31CD8C0 | read-only | secondary | secondary
Handle Coordinator Failure
Because our application connection string includes both coordinator hosts with the option
target_session_attrs=read-write, the database client will connect to whichever of these servers supports
both reads and writes.
However if we use the same trick with the pg_control file to crash our primary coordinator, we can watch
how the monitor promotes the secondary.
$ docker-compose exec coord0a rm /tmp/pgaf/global/pg_control
$ docker-compose exec coord0a /usr/lib/postgresql/14/bin/pg_ctl stop -D /tmp/pgaf
After some time, coordinator A's keeper heals it, and the cluster converges in this state:
$ docker-compose exec monitor pg_autoctl show state
Name | Node | Host:Port | TLI: LSN | Connection | Reported State | Assigned State
---------+-------+---------------+----------------+--------------+---------------------+--------------------
coord0a | 0/3 | coord0a:5432 | 2: 0/50000D8 | read-only | secondary | secondary
coord0b | 0/4 | coord0b:5432 | 2: 0/50000D8 | read-write | primary | primary
worker1a | 1/1 | worker1a:5432 | 2: 0/504C520 | read-only | secondary | secondary
worker1b | 1/2 | worker1b:5432 | 2: 0/504C520 | read-write | primary | primary
worker2b | 2/7 | worker2b:5432 | 2: 0/50FF130 | read-only | secondary | secondary
worker2a | 2/8 | worker2a:5432 | 2: 0/50FF130 | read-write | primary | primary
worker3a | 3/5 | worker3a:5432 | 1: 0/31CD8C0 | read-write | primary | primary
worker3b | 3/6 | worker3b:5432 | 1: 0/31CD8C0 | read-only | secondary | secondary
We can check that the data is still available through the new coordinator node too:
$ docker-compose exec app psql -c 'select count(*) from companies;'
count
-------
75
Cleanup
To dispose of the entire tutorial environment, just use the following command:
$ docker-compose down
Next steps
As mentioned in the first section of this tutorial, the way we use docker-compose here is not meant to be
production ready. It's useful to understand and play with a distributed system such as Citus though, and
makes it simple to introduce faults and see how the pg_auto_failover High Availability reacts to those
faults.
One obvious missing element to better test the system is the lack of persistent volumes in our
docker-compose based test rig. It is possible to create external volumes and use them for each node in
the docker-compose definition. This allows restarting nodes over the same data set.
See the command pg_autoctl do tmux compose session for more details about how to run a docker-compose
test environment with docker-compose, including external volumes for each node.
Now is a good time to go read Citus Documentation too, so that you know how to use this cluster you just
created!
MANUAL PAGES
The pg_autoctl tool hosts many commands and sub-commands. Each of them have their own manual page.
pg_autoctl
pg_autoctl - control a pg_auto_failover node
Synopsis
pg_autoctl provides the following commands:
pg_autoctl
+ create Create a pg_auto_failover node, or formation
+ drop Drop a pg_auto_failover node, or formation
+ config Manages the pg_autoctl configuration
+ show Show pg_auto_failover information
+ enable Enable a feature on a formation
+ disable Disable a feature on a formation
+ get Get a pg_auto_failover node, or formation setting
+ set Set a pg_auto_failover node, or formation setting
+ perform Perform an action orchestrated by the monitor
activate Activate a Citus worker from the Citus coordinator
run Run the pg_autoctl service (monitor or keeper)
stop signal the pg_autoctl service for it to stop
reload signal the pg_autoctl for it to reload its configuration
status Display the current status of the pg_autoctl service
help print help message
version print pg_autoctl version
pg_autoctl create
monitor Initialize a pg_auto_failover monitor node
postgres Initialize a pg_auto_failover standalone postgres node
coordinator Initialize a pg_auto_failover citus coordinator node
worker Initialize a pg_auto_failover citus worker node
formation Create a new formation on the pg_auto_failover monitor
pg_autoctl drop
monitor Drop the pg_auto_failover monitor
node Drop a node from the pg_auto_failover monitor
formation Drop a formation on the pg_auto_failover monitor
pg_autoctl config
check Check pg_autoctl configuration
get Get the value of a given pg_autoctl configuration variable
set Set the value of a given pg_autoctl configuration variable
pg_autoctl show
uri Show the postgres uri to use to connect to pg_auto_failover nodes
events Prints monitor's state of nodes in a given formation and group
state Prints monitor's state of nodes in a given formation and group
settings Print replication settings for a formation from the monitor
standby-names Prints synchronous_standby_names for a given group
file List pg_autoctl internal files (config, state, pid)
systemd Print systemd service file for this node
pg_autoctl enable
secondary Enable secondary nodes on a formation
maintenance Enable Postgres maintenance mode on this node
ssl Enable SSL configuration on this node
monitor Enable a monitor for this node to be orchestrated from
pg_autoctl disable
secondary Disable secondary nodes on a formation
maintenance Disable Postgres maintenance mode on this node
ssl Disable SSL configuration on this node
monitor Disable the monitor for this node
pg_autoctl get
+ node get a node property from the pg_auto_failover monitor
+ formation get a formation property from the pg_auto_failover monitor
pg_autoctl get node
replication-quorum get replication-quorum property from the monitor
candidate-priority get candidate property from the monitor
pg_autoctl get formation
settings get replication settings for a formation from the monitor
number-sync-standbys get number_sync_standbys for a formation from the monitor
pg_autoctl set
+ node set a node property on the monitor
+ formation set a formation property on the monitor
pg_autoctl set node
metadata set metadata on the monitor
replication-quorum set replication-quorum property on the monitor
candidate-priority set candidate property on the monitor
pg_autoctl set formation
number-sync-standbys set number-sync-standbys for a formation on the monitor
pg_autoctl perform
failover Perform a failover for given formation and group
switchover Perform a switchover for given formation and group
promotion Perform a failover that promotes a target node
Description
The pg_autoctl tool is the client tool provided by pg_auto_failover to create and manage Postgres nodes
and the pg_auto_failover monitor node. The command is built with many sub-commands that each have their
own manual page.
Help
To get the full recursive list of supported commands, use:
pg_autoctl help
Version
To grab the version of pg_autoctl that you're using, use:
pg_autoctl --version
pg_autoctl version
A typical output would be:
pg_autoctl version 1.4.2
pg_autoctl extension version 1.4
compiled with PostgreSQL 12.3 on x86_64-apple-darwin16.7.0, compiled by Apple LLVM version 8.1.0 (clang-802.0.42), 64-bit
compatible with Postgres 10, 11, 12, and 13
The version is also available as a JSON document when using the --json option:
pg_autoctl --version --json
pg_autoctl version --json
A typical JSON output would be:
{
"pg_autoctl": "1.4.2",
"pgautofailover": "1.4",
"pg_major": "12",
"pg_version": "12.3",
"pg_version_str": "PostgreSQL 12.3 on x86_64-apple-darwin16.7.0, compiled by Apple LLVM version 8.1.0 (clang-802.0.42), 64-bit",
"pg_version_num": 120003
}
This is for version 1.4.2 of pg_auto_failover. This particular version of the pg_autoctl client tool has
been compiled using libpq for PostgreSQL 12.3 and is compatible with Postgres 10, 11, 12, and 13.
Environment
PG_AUTOCTL_DEBUG
When this environment variable is set (to anything) then pg_autoctl allows more commands. Use with
care, this opens abilities to destroy your production clusters.
pg_autoctl create
pg_autoctl create - Create a pg_auto_failover node, or formation
pg_autoctl create monitor
pg_autoctl create monitor - Initialize a pg_auto_failover monitor node
Synopsis
This command initializes a PostgreSQL cluster and installs the pgautofailover extension so that it's
possible to use the new instance to monitor PostgreSQL services:
usage: pg_autoctl create monitor [ --pgdata --pgport --pgctl --hostname ]
--pgctl path to pg_ctl
--pgdata path to data directory
--pgport PostgreSQL's port number
--hostname hostname by which postgres is reachable
--auth authentication method for connections from data nodes
--skip-pg-hba skip editing pg_hba.conf rules
--run create node then run pg_autoctl service
--ssl-self-signed setup network encryption using self signed certificates (does NOT protect against MITM)
--ssl-mode use that sslmode in connection strings
--ssl-ca-file set the Postgres ssl_ca_file to that file path
--ssl-crl-file set the Postgres ssl_crl_file to that file path
--no-ssl don't enable network encryption (NOT recommended, prefer --ssl-self-signed)
--server-key set the Postgres ssl_key_file to that file path
--server-cert set the Postgres ssl_cert_file to that file path
Description
The pg_autoctl tool is the client tool provided by pg_auto_failover to create and manage Postgres nodes
and the pg_auto_failover monitor node. The command is built with many sub-commands that each have their
own manual page.
Options
The following options are available to pg_autoctl create monitor:
--pgctl
Path to the pg_ctl tool to use for the version of PostgreSQL you want to use.
Defaults to the pg_ctl found in the PATH when there is a single entry for pg_ctl in the PATH.
Check your setup using which -a pg_ctl.
When using an RPM based distribution such as RHEL or CentOS, the path would usually be
/usr/pgsql-13/bin/pg_ctl for Postgres 13.
When using a debian based distribution such as debian or ubuntu, the path would usually be
/usr/lib/postgresql/13/bin/pg_ctl for Postgres 13. Those distributions also use the package
postgresql-common which provides /usr/bin/pg_config. This tool can be automatically used by
pg_autoctl to discover the default version of Postgres to use on your setup.
--pgdata
Location where to initialize a Postgres database cluster, using either pg_ctl initdb or
pg_basebackup. Defaults to the environment variable PGDATA.
--pgport
Postgres port to use, defaults to 5432.
--hostname
Hostname or IP address (both v4 and v6 are supported) to use from any other node to connect to
this node.
When not provided, a default value is computed by running the following algorithm.
1. We get this machine's "public IP" by opening a connection to the 8.8.8.8:53 public service.
Then we get TCP/IP client address that has been used to make that connection.
2. We then do a reverse DNS lookup on the IP address found in the previous step to fetch a
hostname for our local machine.
3. If the reverse DNS lookup is successful , then pg_autoctl does a forward DNS lookup of that
hostname.
When the forward DNS lookup response in step 3. is an IP address found in one of our local network
interfaces, then pg_autoctl uses the hostname found in step 2. as the default --hostname.
Otherwise it uses the IP address found in step 1.
You may use the --hostname command line option to bypass the whole DNS lookup based process and
force the local node name to a fixed value.
--auth Authentication method used by pg_autoctl when editing the Postgres HBA file to open connections to
other nodes. No default value, must be provided by the user. The value --trust is only a good
choice for testing and evaluation of pg_auto_failover, see Security settings for pg_auto_failover
for more information.
--skip-pg-hba
When this option is used then pg_autoctl refrains from any editing of the Postgres HBA file.
Please note that editing the HBA file is still needed so that other nodes can connect using either
read privileges or replication streaming privileges.
When --skip-pg-hba is used, pg_autoctl still outputs the HBA entries it needs in the logs, it only
skips editing the HBA file.
--run Immediately run the pg_autoctl service after having created this node.
--ssl-self-signed
Generate SSL self-signed certificates to provide network encryption. This does not protect against
man-in-the-middle kinds of attacks. See Security settings for pg_auto_failover for more about our
SSL settings.
--ssl-mode
SSL Mode used by pg_autoctl when connecting to other nodes, including when connecting for
streaming replication.
--ssl-ca-file
Set the Postgres ssl_ca_file to that file path.
--ssl-crl-file
Set the Postgres ssl_crl_file to that file path.
--no-ssl
Don't enable network encryption. This is not recommended, prefer --ssl-self-signed.
--server-key
Set the Postgres ssl_key_file to that file path.
--server-cert
Set the Postgres ssl_cert_file to that file path.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_CONFIG
Can be set to the absolute path to the pg_config Postgres tool. This is mostly used in the context of
building extensions, though it can be a useful way to select a Postgres version when several are
installed on the same system.
PATH
Used the usual way mostly. Some entries that are searched in the PATH by the pg_autoctl command are
expected to be found only once, to avoid mistakes with Postgres major versions.
PGHOST, PGPORT, PGDATABASE, PGUSER, PGCONNECT_TIMEOUT, ...
See the Postgres docs about Environment Variables for details.
TMPDIR
The pgcopydb command creates all its work files and directories in ${TMPDIR}/pgcopydb, and defaults to
/tmp/pgcopydb.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
pg_autoctl create postgres
pg_autoctl create postgres - Initialize a pg_auto_failover postgres node
Synopsis
The command pg_autoctl create postgres initializes a standalone Postgres node to a pg_auto_failover
monitor. The monitor is then handling auto-failover for this Postgres node (as soon as a secondary has
been registered too, and is known to be healthy).
usage: pg_autoctl create postgres
--pgctl path to pg_ctl
--pgdata path to data directory
--pghost PostgreSQL's hostname
--pgport PostgreSQL's port number
--listen PostgreSQL's listen_addresses
--username PostgreSQL's username
--dbname PostgreSQL's database name
--name pg_auto_failover node name
--hostname hostname used to connect from the other nodes
--formation pg_auto_failover formation
--monitor pg_auto_failover Monitor Postgres URL
--auth authentication method for connections from monitor
--skip-pg-hba skip editing pg_hba.conf rules
--pg-hba-lan edit pg_hba.conf rules for --dbname in detected LAN
--ssl-self-signed setup network encryption using self signed certificates (does NOT protect against MITM)
--ssl-mode use that sslmode in connection strings
--ssl-ca-file set the Postgres ssl_ca_file to that file path
--ssl-crl-file set the Postgres ssl_crl_file to that file path
--no-ssl don't enable network encryption (NOT recommended, prefer --ssl-self-signed)
--server-key set the Postgres ssl_key_file to that file path
--server-cert set the Postgres ssl_cert_file to that file path
--candidate-priority priority of the node to be promoted to become primary
--replication-quorum true if node participates in write quorum
--maximum-backup-rate maximum transfer rate of data transferred from the server during initial sync
Description
Three different modes of initialization are supported by this command, corresponding to as many
implementation strategies.
1. Initialize a primary node from scratch
This happens when --pgdata (or the environment variable PGDATA) points to an non-existing or empty
directory. Then the given --hostname is registered to the pg_auto_failover --monitor as a member of
the --formation.
The monitor answers to the registration call with a state to assign to the new member of the group,
either SINGLE or WAIT_STANDBY. When the assigned state is SINGLE, then pg_autoctl create postgres
proceeds to initialize a new PostgreSQL instance.
2. Initialize an already existing primary server
This happens when --pgdata (or the environment variable PGDATA) points to an already existing
directory that belongs to a PostgreSQL instance. The standard PostgreSQL tool pg_controldata is
used to recognize whether the directory belongs to a PostgreSQL instance.
In that case, the given --hostname is registered to the monitor in the tentative SINGLE state. When
the given --formation and --group is currently empty, then the monitor accepts the registration and
the pg_autoctl create prepares the already existing primary server for pg_auto_failover.
3. Initialize a secondary node from scratch
This happens when --pgdata (or the environment variable PGDATA) points to a non-existing or empty
directory, and when the monitor registration call assigns the state WAIT_STANDBY in step 1.
In that case, the pg_autoctl create command steps through the initial states of registering a
secondary server, which includes preparing the primary server PostgreSQL HBA rules and creating a
replication slot.
When the command ends successfully, a PostgreSQL secondary server has been created with
pg_basebackup and is now started, catching-up to the primary server.
4. Initialize a secondary node from an existing data directory
When the data directory pointed to by the option --pgdata or the environment variable PGDATA
already exists, then pg_auto_failover verifies that the system identifier matches the one of the
other nodes already existing in the same group.
The system identifier can be obtained with the command pg_controldata. All nodes in a physical
replication setting must have the same system identifier, and so in pg_auto_failover all the nodes
in a same group have that constraint too.
When the system identifier matches the already registered system identifier of other nodes in the
same group, then the node is set-up as a standby and Postgres is started with the primary conninfo
pointed at the current primary.
The --auth option allows setting up authentication method to be used when monitor node makes a connection
to data node with pgautofailover_monitor user. As with the pg_autoctl create monitor command, you could
use --auth trust when playing with pg_auto_failover at first and consider something production grade
later. Also, consider using --skip-pg-hba if you already have your own provisioning tools with a security
compliance process.
See Security settings for pg_auto_failover for notes on .pgpass
Options
The following options are available to pg_autoctl create postgres:
--pgctl
Path to the pg_ctl tool to use for the version of PostgreSQL you want to use.
Defaults to the pg_ctl found in the PATH when there is a single entry for pg_ctl in the PATH.
Check your setup using which -a pg_ctl.
When using an RPM based distribution such as RHEL or CentOS, the path would usually be
/usr/pgsql-13/bin/pg_ctl for Postgres 13.
When using a debian based distribution such as debian or ubuntu, the path would usually be
/usr/lib/postgresql/13/bin/pg_ctl for Postgres 13. Those distributions also use the package
postgresql-common which provides /usr/bin/pg_config. This tool can be automatically used by
pg_autoctl to discover the default version of Postgres to use on your setup.
--pgdata
Location where to initialize a Postgres database cluster, using either pg_ctl initdb or
pg_basebackup. Defaults to the environment variable PGDATA.
--pghost
Hostname to use when connecting to the local Postgres instance from the pg_autoctl process. By
default, this field is left blank in the connection string, allowing to use Unix Domain Sockets
with the default path compiled in your libpq version, usually provided by the Operating System.
That would be /var/run/postgresql when using debian or ubuntu.
--pgport
Postgres port to use, defaults to 5432.
--listen
PostgreSQL's listen_addresses to setup. At the moment only one address is supported in this
command line option.
--username
PostgreSQL's username to use when connecting to the local Postgres instance to manage it.
--dbname
PostgreSQL's database name to use in your application. Defaults to being the same as the
--username, or to postgres when none of those options are used.
--name Node name used on the monitor to refer to this node. The hostname is a technical information, and
given Postgres requirements on the HBA setup and DNS resolution (both forward and reverse
lookups), IP addresses are often used for the hostname.
The --name option allows using a user-friendly name for your Postgres nodes.
--hostname
Hostname or IP address (both v4 and v6 are supported) to use from any other node to connect to
this node.
When not provided, a default value is computed by running the following algorithm.
1. We get this machine's "public IP" by opening a connection to the given monitor hostname or
IP address. Then we get TCP/IP client address that has been used to make that connection.
2. We then do a reverse DNS lookup on the IP address found in the previous step to fetch a
hostname for our local machine.
3. If the reverse DNS lookup is successful , then pg_autoctl does a forward DNS lookup of that
hostname.
When the forward DNS lookup response in step 3. is an IP address found in one of our local network
interfaces, then pg_autoctl uses the hostname found in step 2. as the default --hostname.
Otherwise it uses the IP address found in step 1.
You may use the --hostname command line option to bypass the whole DNS lookup based process and
force the local node name to a fixed value.
--formation
Formation to register the node into on the monitor. Defaults to the default formation, that is
automatically created in the monitor in the pg_autoctl create monitor command.
--monitor
Postgres URI used to connect to the monitor. Must use the autoctl_node username and target the
pg_auto_failover database name. It is possible to show the Postgres URI from the monitor node
using the command pg_autoctl show uri.
--auth Authentication method used by pg_autoctl when editing the Postgres HBA file to open connections to
other nodes. No default value, must be provided by the user. The value --trust is only a good
choice for testing and evaluation of pg_auto_failover, see Security settings for pg_auto_failover
for more information.
--skip-pg-hba
When this option is used then pg_autoctl refrains from any editing of the Postgres HBA file.
Please note that editing the HBA file is still needed so that other nodes can connect using either
read privileges or replication streaming privileges.
When --skip-pg-hba is used, pg_autoctl still outputs the HBA entries it needs in the logs, it only
skips editing the HBA file.
--pg-hba-lan
When this option is used pg_autoctl determines the local IP address used to connect to the
monitor, and retrieves its netmask, and uses that to compute your local area network CIDR. This
CIDR is then opened for connections in the Postgres HBA rules.
For instance, when the monitor resolves to 192.168.0.1 and your local Postgres node uses an
interface with IP address 192.168.0.2/255.255.255.0 to connect to the monitor, then the LAN CIDR
is computed to be 192.168.0.0/24.
--candidate-priority
Sets this node replication setting for candidate priority to the given value (between 0 and 100)
at node registration on the monitor. Defaults to 50.
--replication-quorum
Sets this node replication setting for replication quorum to the given value (either true or
false) at node registration on the monitor. Defaults to true, which enables synchronous
replication.
--maximum-backup-rate
Sets the maximum transfer rate of data transferred from the server during initial sync. This is
used by pg_basebackup. Defaults to 100M.
--run Immediately run the pg_autoctl service after having created this node.
--ssl-self-signed
Generate SSL self-signed certificates to provide network encryption. This does not protect against
man-in-the-middle kinds of attacks. See Security settings for pg_auto_failover for more about our
SSL settings.
--ssl-mode
SSL Mode used by pg_autoctl when connecting to other nodes, including when connecting for
streaming replication.
--ssl-ca-file
Set the Postgres ssl_ca_file to that file path.
--ssl-crl-file
Set the Postgres ssl_crl_file to that file path.
--no-ssl
Don't enable network encryption. This is not recommended, prefer --ssl-self-signed.
--server-key
Set the Postgres ssl_key_file to that file path.
--server-cert
Set the Postgres ssl_cert_file to that file path.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
PG_AUTOCTL_NODE_NAME
Node name to register to the monitor, can be used instead of the --name option.
PG_AUTOCTL_REPLICATION_QUORUM
Can be used instead of the --replication-quorum option.
PG_AUTOCTL_CANDIDATE_PRIORITY
Can be used instead of the --candidate-priority option.
PG_CONFIG
Can be set to the absolute path to the pg_config Postgres tool. This is mostly used in the context of
building extensions, though it can be a useful way to select a Postgres version when several are
installed on the same system.
PATH
Used the usual way mostly. Some entries that are searched in the PATH by the pg_autoctl command are
expected to be found only once, to avoid mistakes with Postgres major versions.
PGHOST, PGPORT, PGDATABASE, PGUSER, PGCONNECT_TIMEOUT, ...
See the Postgres docs about Environment Variables for details.
TMPDIR
The pgcopydb command creates all its work files and directories in ${TMPDIR}/pgcopydb, and defaults to
/tmp/pgcopydb.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
pg_autoctl create coordinator
pg_autoctl create coordinator - Initialize a pg_auto_failover coordinator node
Synopsis
The command pg_autoctl create coordinator initializes a pg_auto_failover Coordinator node for a Citus
formation. The coordinator is special in a Citus formation: that's where the client application connects
to either to manage the formation and the sharding of the tables, or for its normal SQL traffic.
The coordinator also has to register every worker in the formation.
usage: pg_autoctl create coordinator
--pgctl path to pg_ctl
--pgdata path to data directory
--pghost PostgreSQL's hostname
--pgport PostgreSQL's port number
--hostname hostname by which postgres is reachable
--listen PostgreSQL's listen_addresses
--username PostgreSQL's username
--dbname PostgreSQL's database name
--name pg_auto_failover node name
--formation pg_auto_failover formation
--monitor pg_auto_failover Monitor Postgres URL
--auth authentication method for connections from monitor
--skip-pg-hba skip editing pg_hba.conf rules
--citus-secondary when used, this worker node is a citus secondary
--citus-cluster name of the Citus Cluster for read-replicas
--ssl-self-signed setup network encryption using self signed certificates (does NOT protect against MITM)
--ssl-mode use that sslmode in connection strings
--ssl-ca-file set the Postgres ssl_ca_file to that file path
--ssl-crl-file set the Postgres ssl_crl_file to that file path
--no-ssl don't enable network encryption (NOT recommended, prefer --ssl-self-signed)
--server-key set the Postgres ssl_key_file to that file path
--server-cert set the Postgres ssl_cert_file to that file path
Description
This commands works the same as the pg_autoctl create postgres command and implements the following extra
steps:
1. adds shared_preload_libraries = citus to the local PostgreSQL instance configuration.
2. enables the whole local area network to connect to the coordinator, by adding an entry for e.g.
192.168.1.0/24 in the PostgreSQL HBA configuration.
3. creates the extension citus in the target database.
IMPORTANT:
The default --dbname is the same as the current system user name, which in many case is going to be
postgres. Please make sure to use the --dbname option with the actual database that you're going to
use with your application.
Citus does not support multiple databases, you have to use the database where Citus is created. When
using Citus, that is essential to the well behaving of worker failover.
Options
See the manual page for pg_autoctl create postgres for the common options. This section now lists the
options that are specific to pg_autoctl create coordinator:
--citus-secondary
Use this option to create a coordinator dedicated to a Citus Secondary cluster.
See Citus Secondaries and read-replica for more information.
--citus-cluster
Use this option to name the Citus Secondary cluster that this coordinator node belongs to. Use the
same cluster name again for the worker nodes that are part of this cluster.
See Citus Secondaries and read-replica for more information.
pg_autoctl create worker
pg_autoctl create worker - Initialize a pg_auto_failover worker node
Synopsis
The command pg_autoctl create worker initializes a pg_auto_failover Worker node for a Citus formation.
The worker is special in a Citus formation: that's where the client application connects to either to
manage the formation and the sharding of the tables, or for its normal SQL traffic.
The worker also has to register every worker in the formation.
usage: pg_autoctl create worker
--pgctl path to pg_ctl
--pgdata path to data director
--pghost PostgreSQL's hostname
--pgport PostgreSQL's port number
--hostname hostname by which postgres is reachable
--listen PostgreSQL's listen_addresses
--proxyport Proxy's port number
--username PostgreSQL's username
--dbname PostgreSQL's database name
--name pg_auto_failover node name
--formation pg_auto_failover formation
--group pg_auto_failover group Id
--monitor pg_auto_failover Monitor Postgres URL
--auth authentication method for connections from monitor
--skip-pg-hba skip editing pg_hba.conf rules
--citus-secondary when used, this worker node is a citus secondary
--citus-cluster name of the Citus Cluster for read-replicas
--ssl-self-signed setup network encryption using self signed certificates (does NOT protect against MITM)
--ssl-mode use that sslmode in connection strings
--ssl-ca-file set the Postgres ssl_ca_file to that file path
--ssl-crl-file set the Postgres ssl_crl_file to that file path
--no-ssl don't enable network encryption (NOT recommended, prefer --ssl-self-signed)
--server-key set the Postgres ssl_key_file to that file path
--server-cert set the Postgres ssl_cert_file to that file path
Description
This commands works the same as the pg_autoctl create postgres command and implements the following extra
steps:
1. adds shared_preload_libraries = citus to the local PostgreSQL instance configuration.
2. creates the extension citus in the target database.
3. gets the coordinator node hostname from the pg_auto_failover monitor.
This operation is retried when it fails, as the coordinator might appear later than some of the
workers when the whole formation is initialized at once, in parallel, on multiple nodes.
4. adds node to the coordinator
This is done in two steps. First, we call the SQL function master_add_inactive_node on the
coordinator, and second, we call the SQL function master_activate_node.
This way allows for easier diagnostics in case things go wrong. In the first step, the network and
authentication setup needs to allow for nodes to connect to each other. In the second step, the
Citus reference tables are distributed to the new node, and this operation has its own set of
failure cases to handle.
IMPORTANT:
The default --dbname is the same as the current system user name, which in many case is going to be
postgres. Please make sure to use the --dbname option with the actual database that you're going to
use with your application.
Citus does not support multiple databases, you have to use the database where Citus is created. When
using Citus, that is essential to the well behaving of worker failover.
Options
See the manual page for pg_autoctl create postgres for the common options. This section now lists the
options that are specific to pg_autoctl create worker:
--proxyport
The --proxyport option allows pg_auto_failover to register the proxy port in the pg_dist_poolinfo
entry for the worker node in its Coordinator, rather than the --pgport entry as would usually be
done.
--citus-secondary
Use this option to create a worker dedicated to a Citus Secondary cluster.
See Citus Secondaries and read-replica for more information.
--citus-cluster
Use this option to name the Citus Secondary cluster that this worker node belongs to. Use the same
cluster name again for the worker nodes that are part of this cluster.
See Citus Secondaries and read-replica for more information.
pg_autoctl create formation
pg_autoctl create formation - Create a new formation on the pg_auto_failover monitor
Synopsis
This command registers a new formation on the monitor, with the specified kind:
usage: pg_autoctl create formation [ --pgdata --monitor --formation --kind --dbname --with-secondary --without-secondary ]
--pgdata path to data directory
--monitor pg_auto_failover Monitor Postgres URL
--formation name of the formation to create
--kind formation kind, either "pgsql" or "citus"
--dbname name for postgres database to use in this formation
--enable-secondary create a formation that has multiple nodes that can be
used for fail over when others have issues
--disable-secondary create a citus formation without nodes to fail over to
--number-sync-standbys minimum number of standbys to confirm write
Description
A single pg_auto_failover monitor may manage any number of formations, each composed of at least one
Postgres service group. This commands creates a new formation so that it is then possible to register
Postgres nodes in the new formation.
Options
The following options are available to pg_autoctl create formation:
--pgdata
Location where to initialize a Postgres database cluster, using either pg_ctl initdb or
pg_basebackup. Defaults to the environment variable PGDATA.
--monitor
Postgres URI used to connect to the monitor. Must use the autoctl_node username and target the
pg_auto_failover database name. It is possible to show the Postgres URI from the monitor node
using the command pg_autoctl show uri.
--formation
Name of the formation to create.
--kind A pg_auto_failover formation could be of kind pgsql or of kind citus. At the moment citus
formation kinds are not managed in the Open Source version of pg_auto_failover.
--dbname
Name of the database to use in the formation, mostly useful to formation kinds citus where the
Citus extension is only installed in a single target database.
--enable-secondary
The formation to be created allows using standby nodes. Defaults to true. Mostly useful for Citus
formations.
--disable-secondary
See --enable-secondary above.
--number-sync-standby
Postgres streaming replication uses synchronous_standby_names to setup how many standby nodes
should have received a copy of the transaction data. When using pg_auto_failover this setup is
handled at the formation level.
Defaults to zero when creating the first two Postgres nodes in a formation in the same group. When
set to zero pg_auto_failover uses synchronous replication only when a standby node is available:
the idea is to allow failover, this setting does not allow proper HA for Postgres.
When adding a third node that participates in the quorum (one primary, two secondaries), the
setting is automatically changed from zero to one.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
pg_autoctl drop
pg_autoctl drop - Drop a pg_auto_failover node, or formation
pg_autoctl drop monitor
pg_autoctl drop monitor - Drop the pg_auto_failover monitor
Synopsis
This command allows to review all the replication settings of a given formation (defaults to 'default' as
usual):
usage: pg_autoctl drop monitor [ --pgdata --destroy ]
--pgdata path to data directory
--destroy also destroy Postgres database
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--destroy
By default the pg_autoctl drop monitor commands does not remove the Postgres database for the
monitor. When using --destroy, the Postgres installation is also deleted.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
pg_autoctl drop node
pg_autoctl drop node - Drop a node from the pg_auto_failover monitor
Synopsis
This command drops a Postgres node from the pg_auto_failover monitor:
usage: pg_autoctl drop node [ [ [ --pgdata ] [ --destroy ] ] | [ --monitor [ [ --hostname --pgport ] | [ --formation --name ] ] ] ]
--pgdata path to data directory
--monitor pg_auto_failover Monitor Postgres URL
--formation pg_auto_failover formation
--name drop the node with the given node name
--hostname drop the node with given hostname and pgport
--pgport drop the node with given hostname and pgport
--destroy also destroy Postgres database
--force force dropping the node from the monitor
--wait how many seconds to wait, default to 60
Description
Two modes of operations are implemented in the pg_autoctl drop node command.
When removing a node that still exists, it is possible to use pg_autoctl drop node --destroy to remove
the node both from the monitor and also delete the local Postgres instance entirely.
When removing a node that doesn't exist physically anymore, or when the VM that used to host the node has
been lost entirely, use either the pair of options --hostname and --pgport or the pair of options
--formation and --name to match the node registration record on the monitor database, and get it removed
from the known list of nodes on the monitor.
Then option --force can be used when the target node to remove does not exist anymore. When a node has
been lost entirely, it's not going to be able to finish the procedure itself, and it is then possible to
instruct the monitor of the situation.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--monitor
Postgres URI used to connect to the monitor. Must use the autoctl_node username and target the
pg_auto_failover database name. It is possible to show the Postgres URI from the monitor node
using the command pg_autoctl show uri.
--hostname
Hostname of the Postgres node to remove from the monitor. Use either --name or --hostname
--pgport, but not both.
--pgport
Port of the Postgres node to remove from the monitor. Use either --name or --hostname --pgport,
but not both.
--name Name of the node to remove from the monitor. Use either --name or --hostname --pgport, but not
both.
--destroy
By default the pg_autoctl drop monitor commands does not remove the Postgres database for the
monitor. When using --destroy, the Postgres installation is also deleted.
--force
By default a node is expected to reach the assigned state DROPPED when it is removed from the
monitor, and has the opportunity to implement clean-up actions. When the target node to remove is
not available anymore, it is possible to use the option --force to immediately remove the node
from the monitor.
--wait How many seconds to wait for the node to be dropped entirely. The command stops when the target
node is not to be found on the monitor anymore, or when the timeout has elapsed, whichever comes
first. The value 0 (zero) disables the timeout and disables waiting entirely, making the command
async.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
PG_AUTOCTL_NODE_NAME
Node name to register to the monitor, can be used instead of the --name option.
PG_AUTOCTL_REPLICATION_QUORUM
Can be used instead of the --replication-quorum option.
PG_AUTOCTL_CANDIDATE_PRIORITY
Can be used instead of the --candidate-priority option.
PG_CONFIG
Can be set to the absolute path to the pg_config Postgres tool. This is mostly used in the context of
building extensions, though it can be a useful way to select a Postgres version when several are
installed on the same system.
PATH
Used the usual way mostly. Some entries that are searched in the PATH by the pg_autoctl command are
expected to be found only once, to avoid mistakes with Postgres major versions.
PGHOST, PGPORT, PGDATABASE, PGUSER, PGCONNECT_TIMEOUT, ...
See the Postgres docs about Environment Variables for details.
TMPDIR
The pgcopydb command creates all its work files and directories in ${TMPDIR}/pgcopydb, and defaults to
/tmp/pgcopydb.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl drop node --destroy --pgdata ./node3
17:52:21 54201 INFO Reaching assigned state "secondary"
17:52:21 54201 INFO Removing node with name "node3" in formation "default" from the monitor
17:52:21 54201 WARN Postgres is not running and we are in state secondary
17:52:21 54201 WARN Failed to update the keeper's state from the local PostgreSQL instance, see above for details.
17:52:21 54201 INFO Calling node_active for node default/4/0 with current state: PostgreSQL is running is false, sync_state is "", latest WAL LSN is 0/0.
17:52:21 54201 INFO FSM transition to "dropped": This node is being dropped from the monitor
17:52:21 54201 INFO Transition complete: current state is now "dropped"
17:52:21 54201 INFO This node with id 4 in formation "default" and group 0 has been dropped from the monitor
17:52:21 54201 INFO Stopping PostgreSQL at "/Users/dim/dev/MS/pg_auto_failover/tmux/node3"
17:52:21 54201 INFO /Applications/Postgres.app/Contents/Versions/12/bin/pg_ctl --pgdata /Users/dim/dev/MS/pg_auto_failover/tmux/node3 --wait stop --mode fast
17:52:21 54201 INFO /Applications/Postgres.app/Contents/Versions/12/bin/pg_ctl status -D /Users/dim/dev/MS/pg_auto_failover/tmux/node3 [3]
17:52:21 54201 INFO pg_ctl: no server running
17:52:21 54201 INFO pg_ctl stop failed, but PostgreSQL is not running anyway
17:52:21 54201 INFO Removing "/Users/dim/dev/MS/pg_auto_failover/tmux/node3"
17:52:21 54201 INFO Removing "/Users/dim/dev/MS/pg_auto_failover/tmux/config/pg_autoctl/Users/dim/dev/MS/pg_auto_failover/tmux/node3/pg_autoctl.cfg"
pg_autoctl drop formation
pg_autoctl drop formation - Drop a formation on the pg_auto_failover monitor
Synopsis
This command drops an existing formation on the monitor:
usage: pg_autoctl drop formation [ --pgdata --formation ]
--pgdata path to data directory
--monitor pg_auto_failover Monitor Postgres URL
--formation name of the formation to drop
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--monitor
Postgres URI used to connect to the monitor. Must use the autoctl_node username and target the
pg_auto_failover database name. It is possible to show the Postgres URI from the monitor node
using the command pg_autoctl show uri.
--formation
Name of the formation to drop from the monitor.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
pg_autoctl config
pg_autoctl config - Manages the pg_autoctl configuration
pg_autoctl config get
pg_autoctl config get - Get the value of a given pg_autoctl configuration variable
Synopsis
This command prints a pg_autoctl configuration setting:
usage: pg_autoctl config get [ --pgdata ] [ --json ] [ section.option ]
--pgdata path to data directory
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--json Output JSON formatted data.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Description
When the argument section.option is used, this is the name of a configuration ooption. The configuration
file for pg_autoctl is stored using the INI format.
When no argument is given to pg_autoctl config get the entire configuration file is given in the output.
To figure out where the configuration file is stored, see pg_autoctl show file and use pg_autoctl show
file --config.
Examples
Without arguments, we get the entire file:
$ pg_autoctl config get --pgdata node1
[pg_autoctl]
role = keeper
monitor = postgres://autoctl_node@localhost:5500/pg_auto_failover?sslmode=prefer
formation = default
group = 0
name = node1
hostname = localhost
nodekind = standalone
[postgresql]
pgdata = /Users/dim/dev/MS/pg_auto_failover/tmux/node1
pg_ctl = /Applications/Postgres.app/Contents/Versions/12/bin/pg_ctl
dbname = demo
host = /tmp
port = 5501
proxyport = 0
listen_addresses = *
auth_method = trust
hba_level = app
[ssl]
active = 1
sslmode = require
cert_file = /Users/dim/dev/MS/pg_auto_failover/tmux/node1/server.crt
key_file = /Users/dim/dev/MS/pg_auto_failover/tmux/node1/server.key
[replication]
maximum_backup_rate = 100M
backup_directory = /Users/dim/dev/MS/pg_auto_failover/tmux/backup/node_1
[timeout]
network_partition_timeout = 20
prepare_promotion_catchup = 30
prepare_promotion_walreceiver = 5
postgresql_restart_failure_timeout = 20
postgresql_restart_failure_max_retries = 3
It is possible to pipe JSON formatted output to the jq command line and filter the result down to a
specific section of the file:
$ pg_autoctl config get --pgdata node1 --json | jq .pg_autoctl
{
"role": "keeper",
"monitor": "postgres://autoctl_node@localhost:5500/pg_auto_failover?sslmode=prefer",
"formation": "default",
"group": 0,
"name": "node1",
"hostname": "localhost",
"nodekind": "standalone"
}
Finally, a single configuration element can be listed:
$ pg_autoctl config get --pgdata node1 ssl.sslmode --json
require
pg_autoctl config set
pg_autoctl config set - Set the value of a given pg_autoctl configuration variable
Synopsis
This command prints a pg_autoctl configuration setting:
usage: pg_autoctl config set [ --pgdata ] [ --json ] section.option [ value ]
--pgdata path to data directory
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--json Output JSON formatted data.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Description
This commands allows to set a pg_autoctl configuration setting to a new value. Most settings are possible
to change and can be reloaded online.
Some of those commands can then be applied with a pg_autoctl reload command to an already running
process.
Settings
pg_autoctl.role
This setting can not be changed. It can be either monitor or keeper and the rest of the configuration
file is read depending on this value.
pg_autoctl.monitor
URI of the pg_autoctl monitor Postgres service. Can be changed with a reload.
To register an existing node to a new monitor, use pg_autoctl disable monitor and then pg_autoctl
enable monitor.
pg_autoctl.formation
Formation to which this node has been registered. Changing this setting is not supported.
pg_autoctl.group
Group in which this node has been registered. Changing this setting is not supported.
pg_autoctl.name
Name of the node as known to the monitor and listed in pg_autoctl show state. Can be changed with a
reload.
pg_autoctl.hostname
Hostname or IP address of the node, as known to the monitor. Can be changed with a reload.
pg_autoctl.nodekind
This setting can not be changed and depends on the command that has been used to create this
pg_autoctl node.
postgresql.pgdata
Directory where the managed Postgres instance is to be created (or found) and managed. Can't be
changed.
postgresql.pg_ctl
Path to the pg_ctl tool used to manage this Postgres instance. Absolute path depends on the major
version of Postgres and looks like /usr/lib/postgresql/13/bin/pg_ctl when using a debian or ubuntu OS.
Can be changed after a major upgrade of Postgres.
postgresql.dbname
Name of the database that is used to connect to Postgres. Can be changed, but then must be changed
manually on the monitor's pgautofailover.formation table with a SQL command.
WARNING:
When using pg_auto_failover enterprise edition with Citus support, this is the database where
pg_autoctl maintains the list of Citus nodes on the coordinator. Using the same database name as
your application that uses Citus is then crucial.
postgresql.host
Hostname to use in connection strings when connecting from the local pg_autoctl process to the local
Postgres database. Defaults to using the Operating System default value for the Unix Domain Socket
directory, either /tmp or when using debian or ubuntu /var/run/postgresql.
Can be changed with a reload.
postgresql.port
Port on which Postgres should be managed. Can be changed offline, between a pg_autoctl stop and a
subsequent pg_autoctl start.
postgresql.listen_addresses
Value to set to Postgres parameter of the same name. At the moment pg_autoctl only supports a single
address for this parameter.
postgresql.auth_method
Authentication method to use when editing HBA rules to allow the Postgres nodes of a formation to
connect to each other, and to the monitor, and to allow the monitor to connect to the nodes.
Can be changed online with a reload, but actually adding new HBA rules requires a restart of the
"node-active" service.
postgresql.hba_level
This setting reflects the choice of --skip-pg-hba or --pg-hba-lan that has been used when creating
this pg_autoctl node. Can be changed with a reload, though the HBA rules that have been previously
added will not get removed.
ssl.active, ssl.sslmode, ssl.cert_file, ssl.key_file, etc
Please use the command pg_autoctl enable ssl or pg_autoctl disable ssl to manage the SSL settings in
the ssl section of the configuration. Using those commands, the settings can be changed online.
replication.maximum_backup_rate
Used as a parameter to pg_basebackup, defaults to 100M. Can be changed with a reload. Changing this
value does not affect an already running pg_basebackup command.
Limiting the bandwidth used by pg_basebackup makes the operation slower, and still has the advantage
of limiting the impact on the disks of the primary server.
replication.backup_directory
Target location of the pg_basebackup command used by pg_autoctl when creating a secondary node. When
done with fetching the data over the network, then pg_autoctl uses the rename(2) system-call to rename
the temporary download location to the target PGDATA location.
The rename(2) system-call is known to be atomic when both the source and the target of the operation
are using the same file system / mount point.
Can be changed online with a reload, will not affect already running pg_basebackup sub-processes.
replication.password
Used as a parameter in the connection string to the upstream Postgres node. The "replication"
connection uses the password set-up in the pg_autoctl configuration file.
Changing the replication.password of a pg_autoctl configuration has no effect on the Postgres database
itself. The password must match what the Postgres upstream node expects, which can be set with the
following SQL command run on the upstream server (primary or other standby node):
alter user pgautofailover_replicator password 'h4ckm3m0r3';
The replication.password can be changed online with a reload, but requires restarting the Postgres
service to be activated. Postgres only reads the primary_conninfo connection string at start-up, up to
and including Postgres 12. With Postgres 13 and following, it is possible to reload this Postgres
parameter.
timeout.network_partition_timeout
Timeout (in seconds) that pg_autoctl waits before deciding that it is on the losing side of a network
partition. When pg_autoctl fails to connect to the monitor and when the local Postgres instance
pg_stat_replication system view is empty, and after this many seconds have passed, then pg_autoctl
demotes itself.
Can be changed with a reload.
timeout.prepare_promotion_catchup
Currently not used in the source code. Can be changed with a reload.
timeout.prepare_promotion_walreceiver
Currently not used in the source code. Can be changed with a reload.
timeout.postgresql_restart_failure_timeout
When pg_autoctl fails to start Postgres for at least this duration from the first attempt, then it
starts reporting that Postgres is not running to the monitor, which might then decide to implement a
failover.
Can be changed with a reload.
timeout.postgresql_restart_failure_max_retries
When pg_autoctl fails to start Postgres for at least this many times then it starts reporting that
Postgres is not running to the monitor, which them might decide to implement a failover.
Can be changed with a reload.
pg_autoctl config check
pg_autoctl config check - Check pg_autoctl configuration
Synopsis
This command implements a very basic list of sanity checks for a pg_autoctl node setup:
usage: pg_autoctl config check [ --pgdata ] [ --json ]
--pgdata path to data directory
--json output data in the JSON format
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--json Output JSON formatted data.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl config check --pgdata node1
18:37:27 63749 INFO Postgres setup for PGDATA "/Users/dim/dev/MS/pg_auto_failover/tmux/node1" is ok, running with PID 5501 and port 99698
18:37:27 63749 INFO Connection to local Postgres ok, using "port=5501 dbname=demo host=/tmp"
18:37:27 63749 INFO Postgres configuration settings required for pg_auto_failover are ok
18:37:27 63749 WARN Postgres 12.1 does not support replication slots on a standby node
18:37:27 63749 INFO Connection to monitor ok, using "postgres://autoctl_node@localhost:5500/pg_auto_failover?sslmode=prefer"
18:37:27 63749 INFO Monitor is running version "1.5.0.1", as expected
pgdata: /Users/dim/dev/MS/pg_auto_failover/tmux/node1
pg_ctl: /Applications/Postgres.app/Contents/Versions/12/bin/pg_ctl
pg_version: 12.3
pghost: /tmp
pgport: 5501
proxyport: 0
pid: 99698
is in recovery: no
Control Version: 1201
Catalog Version: 201909212
System Identifier: 6941034382470571312
Latest checkpoint LSN: 0/6000098
Postmaster status: ready
pg_autoctl show
pg_autoctl show - Show pg_auto_failover information
pg_autoctl show uri
pg_autoctl show uri - Show the postgres uri to use to connect to pg_auto_failover nodes
Synopsis
This command outputs the monitor or the coordinator Postgres URI to use from an application to connect to
Postgres:
usage: pg_autoctl show uri [ --pgdata --monitor --formation --json ]
--pgdata path to data directory
--monitor monitor uri
--formation show the coordinator uri of given formation
--json output data in the JSON format
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--monitor
Postgres URI used to connect to the monitor. Must use the autoctl_node username and target the
pg_auto_failover database name. It is possible to show the Postgres URI from the monitor node
using the command pg_autoctl show uri.
Defaults to the value of the environment variable PG_AUTOCTL_MONITOR.
--formation
When --formation is used, lists the Postgres URIs of all known formations on the monitor.
--json Output a JSON formatted data instead of a table formatted list.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl show uri
Type | Name | Connection String
-------------+---------+-------------------------------
monitor | monitor | postgres://autoctl_node@localhost:5500/pg_auto_failover
formation | default | postgres://localhost:5502,localhost:5503,localhost:5501/demo?target_session_attrs=read-write&sslmode=prefer
$ pg_autoctl show uri --formation monitor
postgres://autoctl_node@localhost:5500/pg_auto_failover
$ pg_autoctl show uri --formation default
postgres://localhost:5503,localhost:5502,localhost:5501/demo?target_session_attrs=read-write&sslmode=prefer
$ pg_autoctl show uri --json
[
{
"uri": "postgres://autoctl_node@localhost:5500/pg_auto_failover",
"name": "monitor",
"type": "monitor"
},
{
"uri": "postgres://localhost:5503,localhost:5502,localhost:5501/demo?target_session_attrs=read-write&sslmode=prefer",
"name": "default",
"type": "formation"
}
]
Multi-hosts Postgres connection strings
PostgreSQL since version 10 includes support for multiple hosts in its connection driver libpq, with the
special target_session_attrs connection property.
This multi-hosts connection string facility allows applications to keep using the same stable connection
string over server-side failovers. That's why pg_autoctl show uri uses that format.
pg_autoctl show events
pg_autoctl show events - Prints monitor's state of nodes in a given formation and group
Synopsis
This command outputs the events that the pg_auto_failover events records about state changes of the
pg_auto_failover nodes managed by the monitor:
usage: pg_autoctl show events [ --pgdata --formation --group --count ]
--pgdata path to data directory
--monitor pg_auto_failover Monitor Postgres URL
--formation formation to query, defaults to 'default'
--group group to query formation, defaults to all
--count how many events to fetch, defaults to 10
--watch display an auto-updating dashboard
--json output data in the JSON format
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--monitor
Postgres URI used to connect to the monitor. Must use the autoctl_node username and target the
pg_auto_failover database name. It is possible to show the Postgres URI from the monitor node
using the command pg_autoctl show uri.
--formation
List the events recorded for nodes in the given formation. Defaults to default.
--count
By default only the last 10 events are printed.
--watch
Take control of the terminal and display the current state of the system and the last events from
the monitor. The display is updated automatically every 500 milliseconds (half a second) and
reacts properly to window size change.
Depending on the terminal window size, a different set of columns is visible in the state part of
the output. See pg_autoctl watch.
--json Output a JSON formatted data instead of a table formatted list.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl show events --count 2 --json
[
{
"nodeid": 1,
"eventid": 15,
"groupid": 0,
"nodehost": "localhost",
"nodename": "node1",
"nodeport": 5501,
"eventtime": "2021-03-18T12:32:36.103467+01:00",
"goalstate": "primary",
"description": "Setting goal state of node 1 \"node1\" (localhost:5501) to primary now that at least one secondary candidate node is healthy.",
"formationid": "default",
"reportedlsn": "0/4000060",
"reportedstate": "wait_primary",
"reportedrepstate": "async",
"candidatepriority": 50,
"replicationquorum": true
},
{
"nodeid": 1,
"eventid": 16,
"groupid": 0,
"nodehost": "localhost",
"nodename": "node1",
"nodeport": 5501,
"eventtime": "2021-03-18T12:32:36.215494+01:00",
"goalstate": "primary",
"description": "New state is reported by node 1 \"node1\" (localhost:5501): \"primary\"",
"formationid": "default",
"reportedlsn": "0/4000110",
"reportedstate": "primary",
"reportedrepstate": "quorum",
"candidatepriority": 50,
"replicationquorum": true
}
]
pg_autoctl show state
pg_autoctl show state - Prints monitor's state of nodes in a given formation and group
Synopsis
This command outputs the current state of the formation and groups registered to the pg_auto_failover
monitor:
usage: pg_autoctl show state [ --pgdata --formation --group ]
--pgdata path to data directory
--monitor pg_auto_failover Monitor Postgres URL
--formation formation to query, defaults to 'default'
--group group to query formation, defaults to all
--local show local data, do not connect to the monitor
--watch display an auto-updating dashboard
--json output data in the JSON format
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--monitor
Postgres URI used to connect to the monitor. Must use the autoctl_node username and target the
pg_auto_failover database name. It is possible to show the Postgres URI from the monitor node
using the command pg_autoctl show uri.
--formation
List the events recorded for nodes in the given formation. Defaults to default.
--group
Limit output to a single group in the formation. Default to including all groups registered in the
target formation.
--local
Print the local state information without connecting to the monitor.
--watch
Take control of the terminal and display the current state of the system and the last events from
the monitor. The display is updated automatically every 500 milliseconds (half a second) and
reacts properly to window size change.
Depending on the terminal window size, a different set of columns is visible in the state part of
the output. See pg_autoctl watch.
--json Output a JSON formatted data instead of a table formatted list.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Description
The pg_autoctl show state output includes the following columns:
• Name
Name of the node.
• Node
Node information. When the formation has a single group (group zero), then this column only
contains the nodeId.
Only Citus formations allow several groups. When using a Citus formation the Node column
contains the groupId and the nodeId, separated by a colon, such as 0:1 for the first coordinator
node.
• Host:Port
Hostname and port number used to connect to the node.
• TLI: LSN
Timeline identifier (TLI) and Postgres Log Sequence Number (LSN).
The LSN is the current position in the Postgres WAL stream. This is a hexadecimal number. See
pg_lsn for more information.
The current timeline is incremented each time a failover happens, or when doing Point In Time
Recovery. A node can only reach the secondary state when it is on the same timeline as its
primary node.
• Connection
This output field contains two bits of information. First, the Postgres connection type that the
node provides, either read-write or read-only. Then the mark ! is added when the monitor has
failed to connect to this node, and ? when the monitor didn't connect to the node yet.
• Reported State
The latest reported FSM state, as reported to the monitor by the pg_autoctl process running on
the Postgres node.
• Assigned State
The assigned FSM state on the monitor. When the assigned state is not the same as the reported
start, then the pg_autoctl process running on the Postgres node might have not retrieved the
assigned state yet, or might still be implementing the FSM transition from the current state to
the assigned state.
Examples
$ pg_autoctl show state
Name | Node | Host:Port | TLI: LSN | Connection | Reported State | Assigned State
------+-------+----------------+----------------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 1: 0/4000678 | read-write | primary | primary
node2 | 2 | localhost:5502 | 1: 0/4000678 | read-only | secondary | secondary
node3 | 3 | localhost:5503 | 1: 0/4000678 | read-only | secondary | secondary
$ pg_autoctl show state --local
Name | Node | Host:Port | TLI: LSN | Connection | Reported State | Assigned State
------+-------+----------------+----------------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 1: 0/4000678 | read-write ? | primary | primary
$ pg_autoctl show state --json
[
{
"health": 1,
"node_id": 1,
"group_id": 0,
"nodehost": "localhost",
"nodename": "node1",
"nodeport": 5501,
"reported_lsn": "0/4000678",
"reported_tli": 1,
"formation_kind": "pgsql",
"candidate_priority": 50,
"replication_quorum": true,
"current_group_state": "primary",
"assigned_group_state": "primary"
},
{
"health": 1,
"node_id": 2,
"group_id": 0,
"nodehost": "localhost",
"nodename": "node2",
"nodeport": 5502,
"reported_lsn": "0/4000678",
"reported_tli": 1,
"formation_kind": "pgsql",
"candidate_priority": 50,
"replication_quorum": true,
"current_group_state": "secondary",
"assigned_group_state": "secondary"
},
{
"health": 1,
"node_id": 3,
"group_id": 0,
"nodehost": "localhost",
"nodename": "node3",
"nodeport": 5503,
"reported_lsn": "0/4000678",
"reported_tli": 1,
"formation_kind": "pgsql",
"candidate_priority": 50,
"replication_quorum": true,
"current_group_state": "secondary",
"assigned_group_state": "secondary"
}
]
pg_autoctl show settings
pg_autoctl show settings - Print replication settings for a formation from the monitor
Synopsis
This command allows to review all the replication settings of a given formation (defaults to 'default' as
usual):
usage: pg_autoctl show settings [ --pgdata ] [ --json ] [ --formation ]
--pgdata path to data directory
--monitor pg_auto_failover Monitor Postgres URL
--json output data in the JSON format
--formation pg_auto_failover formation
Description
See also pg_autoctl get formation settings which is a synonym.
The output contains setting and values that apply at different contexts, as shown here with a formation
of four nodes, where node_4 is not participating in the replication quorum and also not a candidate for
failover:
$ pg_autoctl show settings
Context | Name | Setting | Value
----------+---------+---------------------------+-------------------------------------------------------------
formation | default | number_sync_standbys | 1
primary | node_1 | synchronous_standby_names | 'ANY 1 (pgautofailover_standby_3, pgautofailover_standby_2)'
node | node_1 | replication quorum | true
node | node_2 | replication quorum | true
node | node_3 | replication quorum | true
node | node_4 | replication quorum | false
node | node_1 | candidate priority | 50
node | node_2 | candidate priority | 50
node | node_3 | candidate priority | 50
node | node_4 | candidate priority | 0
Three replication settings context are listed:
1. The "formation" context contains a single entry, the value of number_sync_standbys for the target
formation.
2. The "primary" context contains one entry per group of Postgres nodes in the formation, and shows
the current value of the synchronous_standby_names Postgres setting as computed by the monitor. It
should match what's currently set on the primary node unless while applying a change, as shown by
the primary being in the APPLY_SETTING state.
3. The "node" context contains two entry per nodes, one line shows the replication quorum setting of
nodes, and another line shows the candidate priority of nodes.
This command gives an overview of all the settings that apply to the current formation.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--monitor
Postgres URI used to connect to the monitor. Must use the autoctl_node username and target the
pg_auto_failover database name. It is possible to show the Postgres URI from the monitor node
using the command pg_autoctl show uri.
Defaults to the value of the environment variable PG_AUTOCTL_MONITOR.
--formation
Show the current replication settings for the given formation. Defaults to the default formation.
--json Output a JSON formatted data instead of a table formatted list.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl show settings
Context | Name | Setting | Value
----------+---------+---------------------------+-------------------------------------------------------------
formation | default | number_sync_standbys | 1
primary | node1 | synchronous_standby_names | 'ANY 1 (pgautofailover_standby_2, pgautofailover_standby_3)'
node | node1 | candidate priority | 50
node | node2 | candidate priority | 50
node | node3 | candidate priority | 50
node | node1 | replication quorum | true
node | node2 | replication quorum | true
node | node3 | replication quorum | true
pg_autoctl show standby-names
pg_autoctl show standby-names - Prints synchronous_standby_names for a given group
Synopsis
This command prints the current value for synchronous_standby_names for the primary Postgres server of
the target group (default 0) in the target formation (default default), as computed by the monitor:
usage: pg_autoctl show standby-names [ --pgdata ] --formation --group
--pgdata path to data directory
--monitor pg_auto_failover Monitor Postgres URL
--formation formation to query, defaults to 'default'
--group group to query formation, defaults to all
--json output data in the JSON format
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--monitor
Postgres URI used to connect to the monitor. Must use the autoctl_node username and target the
pg_auto_failover database name. It is possible to show the Postgres URI from the monitor node
using the command pg_autoctl show uri.
Defaults to the value of the environment variable PG_AUTOCTL_MONITOR.
--formation
Show the current synchronous_standby_names value for the given formation. Defaults to the default
formation.
--group
Show the current synchronous_standby_names value for the given group in the given formation.
Defaults to group 0.
--json Output a JSON formatted data instead of a table formatted list.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl show standby-names
'ANY 1 (pgautofailover_standby_2, pgautofailover_standby_3)'
$ pg_autoctl show standby-names --json
{
"formation": "default",
"group": 0,
"synchronous_standby_names": "ANY 1 (pgautofailover_standby_2, pgautofailover_standby_3)"
}
pg_autoctl show file
pg_autoctl show file - List pg_autoctl internal files (config, state, pid)
Synopsis
This command the files that pg_autoctl uses internally for its own configuration, state, and pid:
usage: pg_autoctl show file [ --pgdata --all --config | --state | --init | --pid --contents ]
--pgdata path to data directory
--all show all pg_autoctl files
--config show pg_autoctl configuration file
--state show pg_autoctl state file
--init show pg_autoctl initialisation state file
--pid show pg_autoctl PID file
--contents show selected file contents
--json output data in the JSON format
Description
The pg_autoctl command follows the XDG Base Directory Specification and places its internal and
configuration files by default in places such as ~/.config/pg_autoctl and ~/.local/share/pg_autoctl.
It is possible to change the default XDG locations by using the environment variables XDG_CONFIG_HOME,
XDG_DATA_HOME, and XDG_RUNTIME_DIR.
Also, pg_config uses sub-directories that are specific to a given PGDATA, making it possible to run
several Postgres nodes on the same machine, which is very practical for testing and development purposes,
though not advised for production setups.
Configuration File
The pg_autoctl configuration file for an instance serving the data directory at /data/pgsql is found at
~/.config/pg_autoctl/data/pgsql/pg_autoctl.cfg, written in the INI format.
It is possible to get the location of the configuration file by using the command pg_autoctl show file
--config --pgdata /data/pgsql and to output its content by using the command pg_autoctl show file
--config --contents --pgdata /data/pgsql.
See also pg_autoctl config get and pg_autoctl config set.
State File
The pg_autoctl state file for an instance serving the data directory at /data/pgsql is found at
~/.local/share/pg_autoctl/data/pgsql/pg_autoctl.state, written in a specific binary format.
This file is not intended to be written by anything else than pg_autoctl itself. In case of state
corruption, see the trouble shooting section of the documentation.
It is possible to get the location of the state file by using the command pg_autoctl show file --state
--pgdata /data/pgsql and to output its content by using the command pg_autoctl show file --state
--contents --pgdata /data/pgsql.
Init State File
The pg_autoctl init state file for an instance serving the data directory at /data/pgsql is found at
~/.local/share/pg_autoctl/data/pgsql/pg_autoctl.init, written in a specific binary format.
This file is not intended to be written by anything else than pg_autoctl itself. In case of state
corruption, see the trouble shooting section of the documentation.
This initialization state file only exists during the initialization of a pg_auto_failover node. In
normal operations, this file does not exist.
It is possible to get the location of the state file by using the command pg_autoctl show file --init
--pgdata /data/pgsql and to output its content by using the command pg_autoctl show file --init
--contents --pgdata /data/pgsql.
PID File
The pg_autoctl PID file for an instance serving the data directory at /data/pgsql is found at
/tmp/pg_autoctl/data/pgsql/pg_autoctl.pid, written in a specific text format.
The PID file is located in a temporary directory by default, or in the XDG_RUNTIME_DIR directory when
this is setup.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--all List all the files that belong to this pg_autoctl node.
--config
Show only the configuration file.
--state
Show only the state file.
--init Show only the init state file, which only exists while the command pg_autoctl create postgres or
the command pg_autoctl create monitor is running, or when than command failed (and can then be
retried).
--pid Show only the pid file.
--contents
When one of the options to show a specific file is in use, then --contents shows the contents of
the selected file instead of showing its absolute file path.
--json Output JSON formatted data.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
The following examples are taken from a QA environment that has been prepared thanks to the make cluster
command made available to the pg_auto_failover contributors. As a result, the XDG environment variables
have been tweaked to obtain a self-contained test:
$ tmux show-env | grep XDG
XDG_CONFIG_HOME=/Users/dim/dev/MS/pg_auto_failover/tmux/config
XDG_DATA_HOME=/Users/dim/dev/MS/pg_auto_failover/tmux/share
XDG_RUNTIME_DIR=/Users/dim/dev/MS/pg_auto_failover/tmux/run
Within that self-contained test location, we can see the following examples.
$ pg_autoctl show file --pgdata ./node1
File | Path
--------+----------------
Config | /Users/dim/dev/MS/pg_auto_failover/tmux/config/pg_autoctl/Users/dim/dev/MS/pg_auto_failover/tmux/node1/pg_autoctl.cfg
State | /Users/dim/dev/MS/pg_auto_failover/tmux/share/pg_autoctl/Users/dim/dev/MS/pg_auto_failover/tmux/node1/pg_autoctl.state
Init | /Users/dim/dev/MS/pg_auto_failover/tmux/share/pg_autoctl/Users/dim/dev/MS/pg_auto_failover/tmux/node1/pg_autoctl.init
Pid | /Users/dim/dev/MS/pg_auto_failover/tmux/run/pg_autoctl/Users/dim/dev/MS/pg_auto_failover/tmux/node1/pg_autoctl.pid
'ANY 1 (pgautofailover_standby_2, pgautofailover_standby_3)'
$ pg_autoctl show file --pgdata node1 --state
/Users/dim/dev/MS/pg_auto_failover/tmux/share/pg_autoctl/Users/dim/dev/MS/pg_auto_failover/tmux/node1/pg_autoctl.state
$ pg_autoctl show file --pgdata node1 --state --contents
Current Role: primary
Assigned Role: primary
Last Monitor Contact: Thu Mar 18 17:32:25 2021
Last Secondary Contact: 0
pg_autoctl state version: 1
group: 0
node id: 1
nodes version: 0
PostgreSQL Version: 1201
PostgreSQL CatVersion: 201909212
PostgreSQL System Id: 6940955496243696337
pg_autoctl show file --pgdata node1 --config --contents --json | jq .pg_autoctl
{
"role": "keeper",
"monitor": "postgres://autoctl_node@localhost:5500/pg_auto_failover?sslmode=prefer",
"formation": "default",
"group": 0,
"name": "node1",
"hostname": "localhost",
"nodekind": "standalone"
}
pg_autoctl show systemd
pg_autoctl show systemd - Print systemd service file for this node
Synopsis
This command outputs a configuration unit that is suitable for registering pg_autoctl as a systemd
service.
Examples
$ pg_autoctl show systemd --pgdata node1
17:38:29 99778 INFO HINT: to complete a systemd integration, run the following commands:
17:38:29 99778 INFO pg_autoctl -q show systemd --pgdata "node1" | sudo tee /etc/systemd/system/pgautofailover.service
17:38:29 99778 INFO sudo systemctl daemon-reload
17:38:29 99778 INFO sudo systemctl enable pgautofailover
17:38:29 99778 INFO sudo systemctl start pgautofailover
[Unit]
Description = pg_auto_failover
[Service]
WorkingDirectory = /Users/dim
Environment = 'PGDATA=node1'
User = dim
ExecStart = /Applications/Postgres.app/Contents/Versions/12/bin/pg_autoctl run
Restart = always
StartLimitBurst = 0
ExecReload = /Applications/Postgres.app/Contents/Versions/12/bin/pg_autoctl reload
[Install]
WantedBy = multi-user.target
To avoid the logs output, use the -q option:
$ pg_autoctl show systemd --pgdata node1 -q
[Unit]
Description = pg_auto_failover
[Service]
WorkingDirectory = /Users/dim
Environment = 'PGDATA=node1'
User = dim
ExecStart = /Applications/Postgres.app/Contents/Versions/12/bin/pg_autoctl run
Restart = always
StartLimitBurst = 0
ExecReload = /Applications/Postgres.app/Contents/Versions/12/bin/pg_autoctl reload
[Install]
WantedBy = multi-user.target
pg_autoctl enable
pg_autoctl enable - Enable a feature on a formation
pg_autoctl enable secondary
pg_autoctl enable secondary - Enable secondary nodes on a formation
Synopsis
This feature makes the most sense when using the Enterprise Edition of pg_auto_failover, which is fully
compatible with Citus formations. When secondary are enabled, then Citus workers creation policy is to
assign a primary node then a standby node for each group. When secondary is disabled the Citus workers
creation policy is to assign only the primary nodes.
usage: pg_autoctl enable secondary [ --pgdata --formation ]
--pgdata path to data directory
--formation Formation to enable secondary on
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--formation
Target formation where to enable secondary feature.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
pg_autoctl enable maintenance
pg_autoctl enable maintenance - Enable Postgres maintenance mode on this node
Synopsis
A pg_auto_failover can be put to a maintenance state. The Postgres node is then still registered to the
monitor, and is known to be unreliable until maintenance is disabled. A node in the maintenance state is
not a candidate for promotion.
Typical use of the maintenance state include Operating System or Postgres reboot, e.g. when applying
security upgrades.
usage: pg_autoctl enable maintenance [ --pgdata --allow-failover ]
--pgdata path to data directory
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--formation
Target formation where to enable secondary feature.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
pg_autoctl show state
Name | Node | Host:Port | LSN | Connection | Current State | Assigned State
------+-------+----------------+-----------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 0/4000760 | read-write | primary | primary
node2 | 2 | localhost:5502 | 0/4000760 | read-only | secondary | secondary
node3 | 3 | localhost:5503 | 0/4000760 | read-only | secondary | secondary
$ pg_autoctl enable maintenance --pgdata node3
12:06:12 47086 INFO Listening monitor notifications about state changes in formation "default" and group 0
12:06:12 47086 INFO Following table displays times when notifications are received
Time | Name | Node | Host:Port | Current State | Assigned State
---------+-------+-------+----------------+---------------------+--------------------
12:06:12 | node1 | 1 | localhost:5501 | primary | join_primary
12:06:12 | node3 | 3 | localhost:5503 | secondary | wait_maintenance
12:06:12 | node3 | 3 | localhost:5503 | wait_maintenance | wait_maintenance
12:06:12 | node1 | 1 | localhost:5501 | join_primary | join_primary
12:06:12 | node3 | 3 | localhost:5503 | wait_maintenance | maintenance
12:06:12 | node1 | 1 | localhost:5501 | join_primary | primary
12:06:13 | node3 | 3 | localhost:5503 | maintenance | maintenance
$ pg_autoctl show state
Name | Node | Host:Port | LSN | Connection | Current State | Assigned State
------+-------+----------------+-----------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 0/4000810 | read-write | primary | primary
node2 | 2 | localhost:5502 | 0/4000810 | read-only | secondary | secondary
node3 | 3 | localhost:5503 | 0/4000810 | none | maintenance | maintenance
pg_autoctl enable ssl
pg_autoctl enable ssl - Enable SSL configuration on this node
Synopsis
It is possible to manage Postgres SSL settings with the pg_autoctl command, both at pg_autoctl create
postgres time and then again to change your mind and update the SSL settings at run-time.
usage: pg_autoctl enable ssl [ --pgdata ] [ --json ]
--pgdata path to data directory
--ssl-self-signed setup network encryption using self signed certificates (does NOT protect against MITM)
--ssl-mode use that sslmode in connection strings
--ssl-ca-file set the Postgres ssl_ca_file to that file path
--ssl-crl-file set the Postgres ssl_crl_file to that file path
--no-ssl don't enable network encryption (NOT recommended, prefer --ssl-self-signed)
--server-key set the Postgres ssl_key_file to that file path
--server-cert set the Postgres ssl_cert_file to that file path
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--ssl-self-signed
Generate SSL self-signed certificates to provide network encryption. This does not protect against
man-in-the-middle kinds of attacks. See Security settings for pg_auto_failover for more about our
SSL settings.
--ssl-mode
SSL Mode used by pg_autoctl when connecting to other nodes, including when connecting for
streaming replication.
--ssl-ca-file
Set the Postgres ssl_ca_file to that file path.
--ssl-crl-file
Set the Postgres ssl_crl_file to that file path.
--no-ssl
Don't enable network encryption. This is not recommended, prefer --ssl-self-signed.
--server-key
Set the Postgres ssl_key_file to that file path.
--server-cert
Set the Postgres ssl_cert_file to that file path.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
pg_autoctl enable monitor
pg_autoctl enable monitor - Enable a monitor for this node to be orchestrated from
Synopsis
It is possible to disable the pg_auto_failover monitor and enable it again online in a running pg_autoctl
Postgres node. The main use-cases where this operation is useful is when the monitor node has to be
replaced, either after a full crash of the previous monitor node, of for migrating to a new monitor node
(hardware replacement, region or zone migration, etc).
usage: pg_autoctl enable monitor [ --pgdata --allow-failover ] postgres://autoctl_node@new.monitor.add.ress/pg_auto_failover
--pgdata path to data directory
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl show state
Name | Node | Host:Port | LSN | Connection | Current State | Assigned State
------+-------+----------------+-----------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 0/4000760 | read-write | primary | primary
node2 | 2 | localhost:5502 | 0/4000760 | read-only | secondary | secondary
$ pg_autoctl enable monitor --pgdata node3 'postgres://autoctl_node@localhost:5500/pg_auto_failover?sslmode=require'
12:42:07 43834 INFO Registered node 3 (localhost:5503) with name "node3" in formation "default", group 0, state "wait_standby"
12:42:07 43834 INFO Successfully registered to the monitor with nodeId 3
12:42:08 43834 INFO Still waiting for the monitor to drive us to state "catchingup"
12:42:08 43834 WARN Please make sure that the primary node is currently running `pg_autoctl run` and contacting the monitor.
$ pg_autoctl show state
Name | Node | Host:Port | LSN | Connection | Current State | Assigned State
------+-------+----------------+-----------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 0/4000810 | read-write | primary | primary
node2 | 2 | localhost:5502 | 0/4000810 | read-only | secondary | secondary
node3 | 3 | localhost:5503 | 0/4000810 | read-only | secondary | secondary
pg_autoctl disable
pg_autoctl disable - Disable a feature on a formation
pg_autoctl disable secondary
pg_autoctl disable secondary - Disable secondary nodes on a formation
Synopsis
This feature makes the most sense when using the Enterprise Edition of pg_auto_failover, which is fully
compatible with Citus formations. When secondary are disabled, then Citus workers creation policy is to
assign a primary node then a standby node for each group. When secondary is disabled the Citus workers
creation policy is to assign only the primary nodes.
usage: pg_autoctl disable secondary [ --pgdata --formation ]
--pgdata path to data directory
--formation Formation to disable secondary on
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--formation
Target formation where to disable secondary feature.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
pg_autoctl disable maintenance
pg_autoctl disable maintenance - Disable Postgres maintenance mode on this node
Synopsis
A pg_auto_failover can be put to a maintenance state. The Postgres node is then still registered to the
monitor, and is known to be unreliable until maintenance is disabled. A node in the maintenance state is
not a candidate for promotion.
Typical use of the maintenance state include Operating System or Postgres reboot, e.g. when applying
security upgrades.
usage: pg_autoctl disable maintenance [ --pgdata --allow-failover ]
--pgdata path to data directory
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--formation
Target formation where to disable secondary feature.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl show state
Name | Node | Host:Port | LSN | Connection | Current State | Assigned State
------+-------+----------------+-----------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 0/4000810 | read-write | primary | primary
node2 | 2 | localhost:5502 | 0/4000810 | read-only | secondary | secondary
node3 | 3 | localhost:5503 | 0/4000810 | none | maintenance | maintenance
$ pg_autoctl disable maintenance --pgdata node3
12:06:37 47542 INFO Listening monitor notifications about state changes in formation "default" and group 0
12:06:37 47542 INFO Following table displays times when notifications are received
Time | Name | Node | Host:Port | Current State | Assigned State
---------+-------+-------+----------------+---------------------+--------------------
12:06:37 | node3 | 3 | localhost:5503 | maintenance | catchingup
12:06:37 | node3 | 3 | localhost:5503 | catchingup | catchingup
12:06:37 | node3 | 3 | localhost:5503 | catchingup | secondary
12:06:37 | node3 | 3 | localhost:5503 | secondary | secondary
$ pg_autoctl show state
Name | Node | Host:Port | LSN | Connection | Current State | Assigned State
------+-------+----------------+-----------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 0/4000848 | read-write | primary | primary
node2 | 2 | localhost:5502 | 0/4000848 | read-only | secondary | secondary
node3 | 3 | localhost:5503 | 0/4000000 | read-only | secondary | secondary
pg_autoctl disable ssl
pg_autoctl disable ssl - Disable SSL configuration on this node
Synopsis
It is possible to manage Postgres SSL settings with the pg_autoctl command, both at pg_autoctl create
postgres time and then again to change your mind and update the SSL settings at run-time.
usage: pg_autoctl disable ssl [ --pgdata ] [ --json ]
--pgdata path to data directory
--ssl-self-signed setup network encryption using self signed certificates (does NOT protect against MITM)
--ssl-mode use that sslmode in connection strings
--ssl-ca-file set the Postgres ssl_ca_file to that file path
--ssl-crl-file set the Postgres ssl_crl_file to that file path
--no-ssl don't disable network encryption (NOT recommended, prefer --ssl-self-signed)
--server-key set the Postgres ssl_key_file to that file path
--server-cert set the Postgres ssl_cert_file to that file path
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--ssl-self-signed
Generate SSL self-signed certificates to provide network encryption. This does not protect against
man-in-the-middle kinds of attacks. See Security settings for pg_auto_failover for more about our
SSL settings.
--ssl-mode
SSL Mode used by pg_autoctl when connecting to other nodes, including when connecting for
streaming replication.
--ssl-ca-file
Set the Postgres ssl_ca_file to that file path.
--ssl-crl-file
Set the Postgres ssl_crl_file to that file path.
--no-ssl
Don't disable network encryption. This is not recommended, prefer --ssl-self-signed.
--server-key
Set the Postgres ssl_key_file to that file path.
--server-cert
Set the Postgres ssl_cert_file to that file path.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
pg_autoctl disable monitor
pg_autoctl disable monitor - Disable the monitor for this node
Synopsis
It is possible to disable the pg_auto_failover monitor and enable it again online in a running pg_autoctl
Postgres node. The main use-cases where this operation is useful is when the monitor node has to be
replaced, either after a full crash of the previous monitor node, of for migrating to a new monitor node
(hardware replacement, region or zone migration, etc).
usage: pg_autoctl disable monitor [ --pgdata --force ]
--pgdata path to data directory
--force force unregistering from the monitor
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--force
The --force covers the two following situations:
1. By default, the command expects to be able to connect to the current monitor. When the
current known monitor in the setup is not running anymore, use --force to skip this step.
2. When pg_autoctl could connect to the monitor and the node is found there, this is normally
an error that prevents from disabling the monitor. Using --force allows the command to drop
the node from the monitor and continue with disabling the monitor.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl show state
Name | Node | Host:Port | LSN | Connection | Current State | Assigned State
------+-------+----------------+-----------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 0/4000148 | read-write | primary | primary
node2 | 2 | localhost:5502 | 0/4000148 | read-only | secondary | secondary
node3 | 3 | localhost:5503 | 0/4000148 | read-only | secondary | secondary
$ pg_autoctl disable monitor --pgdata node3
12:41:21 43039 INFO Found node 3 "node3" (localhost:5503) on the monitor
12:41:21 43039 FATAL Use --force to remove the node from the monitor
$ pg_autoctl disable monitor --pgdata node3 --force
12:41:32 43219 INFO Removing node 3 "node3" (localhost:5503) from monitor
$ pg_autoctl show state
Name | Node | Host:Port | LSN | Connection | Current State | Assigned State
------+-------+----------------+-----------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 0/4000760 | read-write | primary | primary
node2 | 2 | localhost:5502 | 0/4000760 | read-only | secondary | secondary
pg_autoctl get
pg_autoctl get - Get a pg_auto_failover node, or formation setting
pg_autoctl get formation settings
pg_autoctl get formation settings - get replication settings for a formation from the monitor
Synopsis
This command prints a pg_autoctl replication settings:
usage: pg_autoctl get formation settings [ --pgdata ] [ --json ] [ --formation ]
--pgdata path to data directory
--json output data in the JSON format
--formation pg_auto_failover formation
Description
See also pg_autoctl show settings which is a synonym.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--json Output JSON formatted data.
--formation
Show replication settings for given formation. Defaults to default.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl get formation settings
Context | Name | Setting | Value
----------+---------+---------------------------+-------------------------------------------------------------
formation | default | number_sync_standbys | 1
primary | node1 | synchronous_standby_names | 'ANY 1 (pgautofailover_standby_2, pgautofailover_standby_3)'
node | node1 | candidate priority | 50
node | node2 | candidate priority | 50
node | node3 | candidate priority | 50
node | node1 | replication quorum | true
node | node2 | replication quorum | true
node | node3 | replication quorum | true
$ pg_autoctl get formation settings --json
{
"nodes": [
{
"value": "true",
"context": "node",
"node_id": 1,
"setting": "replication quorum",
"group_id": 0,
"nodename": "node1"
},
{
"value": "true",
"context": "node",
"node_id": 2,
"setting": "replication quorum",
"group_id": 0,
"nodename": "node2"
},
{
"value": "true",
"context": "node",
"node_id": 3,
"setting": "replication quorum",
"group_id": 0,
"nodename": "node3"
},
{
"value": "50",
"context": "node",
"node_id": 1,
"setting": "candidate priority",
"group_id": 0,
"nodename": "node1"
},
{
"value": "50",
"context": "node",
"node_id": 2,
"setting": "candidate priority",
"group_id": 0,
"nodename": "node2"
},
{
"value": "50",
"context": "node",
"node_id": 3,
"setting": "candidate priority",
"group_id": 0,
"nodename": "node3"
}
],
"primary": [
{
"value": "'ANY 1 (pgautofailover_standby_2, pgautofailover_standby_3)'",
"context": "primary",
"node_id": 1,
"setting": "synchronous_standby_names",
"group_id": 0,
"nodename": "node1"
}
],
"formation": {
"value": "1",
"context": "formation",
"node_id": null,
"setting": "number_sync_standbys",
"group_id": null,
"nodename": "default"
}
}
pg_autoctl get formation number-sync-standbys
pg_autoctl get formation number-sync-standbys - get number_sync_standbys for a formation from the monitor
Synopsis
This command prints a pg_autoctl replication settings for number sync standbys:
usage: pg_autoctl get formation number-sync-standbys [ --pgdata ] [ --json ] [ --formation ]
--pgdata path to data directory
--json output data in the JSON format
--formation pg_auto_failover formation
Description
See also pg_autoctl show settings for the full list of replication settings.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--json Output JSON formatted data.
--formation
Show replication settings for given formation. Defaults to default.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl get formation number-sync-standbys
1
$ pg_autoctl get formation number-sync-standbys --json
{
"number-sync-standbys": 1
}
pg_autoctl get node replication-quorum
pg_autoctl get replication-quorum - get replication-quorum property from the monitor
Synopsis
This command prints pg_autoctl replication quorum for a given node:
usage: pg_autoctl get node replication-quorum [ --pgdata ] [ --json ] [ --formation ] [ --name ]
--pgdata path to data directory
--formation pg_auto_failover formation
--name pg_auto_failover node name
--json output data in the JSON format
Description
See also pg_autoctl show settings for the full list of replication settings.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--json Output JSON formatted data.
--formation
Show replication settings for given formation. Defaults to default.
--name Show replication settings for given node, selected by name.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl get node replication-quorum --name node1
true
$ pg_autoctl get node replication-quorum --name node1 --json
{
"name": "node1",
"replication-quorum": true
}
pg_autoctl get node candidate-priority
pg_autoctl get candidate-priority - get candidate-priority property from the monitor
Synopsis
This command prints pg_autoctl candidate priority for a given node:
usage: pg_autoctl get node candidate-priority [ --pgdata ] [ --json ] [ --formation ] [ --name ]
--pgdata path to data directory
--formation pg_auto_failover formation
--name pg_auto_failover node name
--json output data in the JSON format
Description
See also pg_autoctl show settings for the full list of replication settings.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--json Output JSON formatted data.
--formation
Show replication settings for given formation. Defaults to default.
--name Show replication settings for given node, selected by name.
Examples
$ pg_autoctl get node candidate-priority --name node1
50
$ pg_autoctl get node candidate-priority --name node1 --json
{
"name": "node1",
"candidate-priority": 50
}
pg_autoctl set
pg_autoctl set - Set a pg_auto_failover node, or formation setting
pg_autoctl set formation number-sync-standbys
pg_autoctl set formation number-sync-standbys - set number_sync_standbys for a formation from the monitor
Synopsis
This command set a pg_autoctl replication settings for number sync standbys:
usage: pg_autoctl set formation number-sync-standbys [ --pgdata ] [ --json ] [ --formation ] <number_sync_standbys>
--pgdata path to data directory
--formation pg_auto_failover formation
--json output data in the JSON format
Description
The pg_auto_failover monitor ensures that at least N+1 candidate standby nodes are registered when
number-sync-standbys is N. This means that to be able to run the following command, at least 3 standby
nodes with a non-zero candidate priority must be registered to the monitor:
$ pg_autoctl set formation number-sync-standbys 2
See also pg_autoctl show settings for the full list of replication settings.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--json Output JSON formatted data.
--formation
Show replication settings for given formation. Defaults to default.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
pg_autoctl set node replication-quorum
pg_autoctl set replication-quorum - set replication-quorum property from the monitor
Synopsis
This command sets pg_autoctl replication quorum for a given node:
usage: pg_autoctl set node replication-quorum [ --pgdata ] [ --json ] [ --formation ] [ --name ] <true|false>
--pgdata path to data directory
--formation pg_auto_failover formation
--name pg_auto_failover node name
--json output data in the JSON format
Description
See also pg_autoctl show settings for the full list of replication settings.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--json Output JSON formatted data.
--formation
Show replication settings for given formation. Defaults to default.
--name Show replication settings for given node, selected by name.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl set node replication-quorum --name node1 false
12:49:37 94092 INFO Waiting for the settings to have been applied to the monitor and primary node
12:49:37 94092 INFO New state is reported by node 1 "node1" (localhost:5501): "apply_settings"
12:49:37 94092 INFO Setting goal state of node 1 "node1" (localhost:5501) to primary after it applied replication properties change.
12:49:37 94092 INFO New state is reported by node 1 "node1" (localhost:5501): "primary"
false
$ pg_autoctl set node replication-quorum --name node1 true --json
12:49:42 94199 INFO Waiting for the settings to have been applied to the monitor and primary node
12:49:42 94199 INFO New state is reported by node 1 "node1" (localhost:5501): "apply_settings"
12:49:42 94199 INFO Setting goal state of node 1 "node1" (localhost:5501) to primary after it applied replication properties change.
12:49:43 94199 INFO New state is reported by node 1 "node1" (localhost:5501): "primary"
{
"replication-quorum": true
}
pg_autoctl set node candidate-priority
pg_autoctl set candidate-priority - set candidate-priority property from the monitor
Synopsis
This command sets the pg_autoctl candidate priority for a given node:
usage: pg_autoctl set node candidate-priority [ --pgdata ] [ --json ] [ --formation ] [ --name ] <priority: 0..100>
--pgdata path to data directory
--formation pg_auto_failover formation
--name pg_auto_failover node name
--json output data in the JSON format
Description
See also pg_autoctl show settings for the full list of replication settings.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--json Output JSON formatted data.
--formation
Show replication settings for given formation. Defaults to default.
--name Show replication settings for given node, selected by name.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl set node candidate-priority --name node1 65
12:47:59 92326 INFO Waiting for the settings to have been applied to the monitor and primary node
12:47:59 92326 INFO New state is reported by node 1 "node1" (localhost:5501): "apply_settings"
12:47:59 92326 INFO Setting goal state of node 1 "node1" (localhost:5501) to primary after it applied replication properties change.
12:47:59 92326 INFO New state is reported by node 1 "node1" (localhost:5501): "primary"
65
$ pg_autoctl set node candidate-priority --name node1 50 --json
12:48:05 92450 INFO Waiting for the settings to have been applied to the monitor and primary node
12:48:05 92450 INFO New state is reported by node 1 "node1" (localhost:5501): "apply_settings"
12:48:05 92450 INFO Setting goal state of node 1 "node1" (localhost:5501) to primary after it applied replication properties change.
12:48:05 92450 INFO New state is reported by node 1 "node1" (localhost:5501): "primary"
{
"candidate-priority": 50
}
pg_autoctl perform
pg_autoctl perform - Perform an action orchestrated by the monitor
pg_autoctl perform failover
pg_autoctl perform failover - Perform a failover for given formation and group
Synopsis
This command starts a Postgres failover orchestration from the pg_auto_failover monitor:
usage: pg_autoctl perform failover [ --pgdata --formation --group ]
--pgdata path to data directory
--formation formation to target, defaults to 'default'
--group group to target, defaults to 0
--wait how many seconds to wait, default to 60
Description
The pg_auto_failover monitor can be used to orchestrate a manual failover, sometimes also known as a
switchover. When doing so, split-brain are prevented thanks to intermediary states being used in the
Finite State Machine.
The pg_autoctl perform failover command waits until the failover is known complete on the monitor, or
until the hard-coded 60s timeout has passed.
The failover orchestration is done in the background by the monitor, so even if the pg_autoctl perform
failover stops on the timeout, the failover orchestration continues at the monitor.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--formation
Formation to target for the operation. Defaults to default.
--group
Postgres group to target for the operation. Defaults to 0, only Citus formations may have more
than one group.
--wait How many seconds to wait for notifications about the promotion. The command stops when the
promotion is finished (a node is primary), or when the timeout has elapsed, whichever comes first.
The value 0 (zero) disables the timeout and allows the command to wait forever.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
PGHOST, PGPORT, PGDATABASE, PGUSER, PGCONNECT_TIMEOUT, ...
See the Postgres docs about Environment Variables for details.
TMPDIR
The pgcopydb command creates all its work files and directories in ${TMPDIR}/pgcopydb, and defaults to
/tmp/pgcopydb.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl perform failover
12:57:30 3635 INFO Listening monitor notifications about state changes in formation "default" and group 0
12:57:30 3635 INFO Following table displays times when notifications are received
Time | Name | Node | Host:Port | Current State | Assigned State
---------+-------+-------+----------------+---------------------+--------------------
12:57:30 | node1 | 1 | localhost:5501 | primary | draining
12:57:30 | node1 | 1 | localhost:5501 | draining | draining
12:57:30 | node2 | 2 | localhost:5502 | secondary | report_lsn
12:57:30 | node3 | 3 | localhost:5503 | secondary | report_lsn
12:57:36 | node3 | 3 | localhost:5503 | report_lsn | report_lsn
12:57:36 | node2 | 2 | localhost:5502 | report_lsn | report_lsn
12:57:36 | node2 | 2 | localhost:5502 | report_lsn | prepare_promotion
12:57:36 | node2 | 2 | localhost:5502 | prepare_promotion | prepare_promotion
12:57:36 | node2 | 2 | localhost:5502 | prepare_promotion | stop_replication
12:57:36 | node1 | 1 | localhost:5501 | draining | demote_timeout
12:57:36 | node3 | 3 | localhost:5503 | report_lsn | join_secondary
12:57:36 | node1 | 1 | localhost:5501 | demote_timeout | demote_timeout
12:57:36 | node3 | 3 | localhost:5503 | join_secondary | join_secondary
12:57:37 | node2 | 2 | localhost:5502 | stop_replication | stop_replication
12:57:37 | node2 | 2 | localhost:5502 | stop_replication | wait_primary
12:57:37 | node1 | 1 | localhost:5501 | demote_timeout | demoted
12:57:37 | node1 | 1 | localhost:5501 | demoted | demoted
12:57:37 | node2 | 2 | localhost:5502 | wait_primary | wait_primary
12:57:37 | node3 | 3 | localhost:5503 | join_secondary | secondary
12:57:37 | node1 | 1 | localhost:5501 | demoted | catchingup
12:57:38 | node3 | 3 | localhost:5503 | secondary | secondary
12:57:38 | node2 | 2 | localhost:5502 | wait_primary | primary
12:57:38 | node1 | 1 | localhost:5501 | catchingup | catchingup
12:57:38 | node2 | 2 | localhost:5502 | primary | primary
$ pg_autoctl show state
Name | Node | Host:Port | LSN | Connection | Current State | Assigned State
------+-------+----------------+-----------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 0/4000F50 | read-only | secondary | secondary
node2 | 2 | localhost:5502 | 0/4000F50 | read-write | primary | primary
node3 | 3 | localhost:5503 | 0/4000F50 | read-only | secondary | secondary
pg_autoctl perform switchover
pg_autoctl perform switchover - Perform a switchover for given formation and group
Synopsis
This command starts a Postgres switchover orchestration from the pg_auto_switchover monitor:
usage: pg_autoctl perform switchover [ --pgdata --formation --group ]
--pgdata path to data directory
--formation formation to target, defaults to 'default'
--group group to target, defaults to 0
Description
The pg_auto_switchover monitor can be used to orchestrate a manual switchover, sometimes also known as a
switchover. When doing so, split-brain are prevented thanks to intermediary states being used in the
Finite State Machine.
The pg_autoctl perform switchover command waits until the switchover is known complete on the monitor, or
until the hard-coded 60s timeout has passed.
The switchover orchestration is done in the background by the monitor, so even if the pg_autoctl perform
switchover stops on the timeout, the switchover orchestration continues at the monitor.
See also pg_autoctl perform failover, a synonym for this command.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--formation
Formation to target for the operation. Defaults to default.
--group
Postgres group to target for the operation. Defaults to 0, only Citus formations may have more
than one group.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
PG_CONFIG
Can be set to the absolute path to the pg_config Postgres tool. This is mostly used in the context of
building extensions, though it can be a useful way to select a Postgres version when several are
installed on the same system.
PATH
Used the usual way mostly. Some entries that are searched in the PATH by the pg_autoctl command are
expected to be found only once, to avoid mistakes with Postgres major versions.
PGHOST, PGPORT, PGDATABASE, PGUSER, PGCONNECT_TIMEOUT, ...
See the Postgres docs about Environment Variables for details.
TMPDIR
The pgcopydb command creates all its work files and directories in ${TMPDIR}/pgcopydb, and defaults to
/tmp/pgcopydb.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
pg_autoctl perform promotion
pg_autoctl perform promotion - Perform a failover that promotes a target node
Synopsis
This command starts a Postgres failover orchestration from the pg_auto_promotion monitor and targets
given node:
usage: pg_autoctl perform promotion [ --pgdata --formation --group ]
--pgdata path to data directory
--formation formation to target, defaults to 'default'
--name node name to target, defaults to current node
--wait how many seconds to wait, default to 60
Description
The pg_auto_promotion monitor can be used to orchestrate a manual promotion, sometimes also known as a
switchover. When doing so, split-brain are prevented thanks to intermediary states being used in the
Finite State Machine.
The pg_autoctl perform promotion command waits until the promotion is known complete on the monitor, or
until the hard-coded 60s timeout has passed.
The promotion orchestration is done in the background by the monitor, so even if the pg_autoctl perform
promotion stops on the timeout, the promotion orchestration continues at the monitor.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--formation
Formation to target for the operation. Defaults to default.
--name Name of the node that should be elected as the new primary node.
--wait How many seconds to wait for notifications about the promotion. The command stops when the
promotion is finished (a node is primary), or when the timeout has elapsed, whichever comes first.
The value 0 (zero) disables the timeout and allows the command to wait forever.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
PG_CONFIG
Can be set to the absolute path to the pg_config Postgres tool. This is mostly used in the context of
building extensions, though it can be a useful way to select a Postgres version when several are
installed on the same system.
PATH
Used the usual way mostly. Some entries that are searched in the PATH by the pg_autoctl command are
expected to be found only once, to avoid mistakes with Postgres major versions.
PGHOST, PGPORT, PGDATABASE, PGUSER, PGCONNECT_TIMEOUT, ...
See the Postgres docs about Environment Variables for details.
TMPDIR
The pgcopydb command creates all its work files and directories in ${TMPDIR}/pgcopydb, and defaults to
/tmp/pgcopydb.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Examples
$ pg_autoctl show state
Name | Node | Host:Port | LSN | Connection | Current State | Assigned State
------+-------+----------------+-----------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 0/4000F88 | read-only | secondary | secondary
node2 | 2 | localhost:5502 | 0/4000F88 | read-write | primary | primary
node3 | 3 | localhost:5503 | 0/4000F88 | read-only | secondary | secondary
$ pg_autoctl perform promotion --name node1
13:08:13 15297 INFO Listening monitor notifications about state changes in formation "default" and group 0
13:08:13 15297 INFO Following table displays times when notifications are received
Time | Name | Node | Host:Port | Current State | Assigned State
---------+-------+-------+----------------+---------------------+--------------------
13:08:13 | node1 | 0/1 | localhost:5501 | secondary | secondary
13:08:13 | node2 | 0/2 | localhost:5502 | primary | draining
13:08:13 | node2 | 0/2 | localhost:5502 | draining | draining
13:08:13 | node1 | 0/1 | localhost:5501 | secondary | report_lsn
13:08:13 | node3 | 0/3 | localhost:5503 | secondary | report_lsn
13:08:19 | node3 | 0/3 | localhost:5503 | report_lsn | report_lsn
13:08:19 | node1 | 0/1 | localhost:5501 | report_lsn | report_lsn
13:08:19 | node1 | 0/1 | localhost:5501 | report_lsn | prepare_promotion
13:08:19 | node1 | 0/1 | localhost:5501 | prepare_promotion | prepare_promotion
13:08:19 | node1 | 0/1 | localhost:5501 | prepare_promotion | stop_replication
13:08:19 | node2 | 0/2 | localhost:5502 | draining | demote_timeout
13:08:19 | node3 | 0/3 | localhost:5503 | report_lsn | join_secondary
13:08:19 | node2 | 0/2 | localhost:5502 | demote_timeout | demote_timeout
13:08:19 | node3 | 0/3 | localhost:5503 | join_secondary | join_secondary
13:08:20 | node1 | 0/1 | localhost:5501 | stop_replication | stop_replication
13:08:20 | node1 | 0/1 | localhost:5501 | stop_replication | wait_primary
13:08:20 | node2 | 0/2 | localhost:5502 | demote_timeout | demoted
13:08:20 | node1 | 0/1 | localhost:5501 | wait_primary | wait_primary
13:08:20 | node3 | 0/3 | localhost:5503 | join_secondary | secondary
13:08:20 | node2 | 0/2 | localhost:5502 | demoted | demoted
13:08:20 | node2 | 0/2 | localhost:5502 | demoted | catchingup
13:08:21 | node3 | 0/3 | localhost:5503 | secondary | secondary
13:08:21 | node1 | 0/1 | localhost:5501 | wait_primary | primary
13:08:21 | node2 | 0/2 | localhost:5502 | catchingup | catchingup
13:08:21 | node1 | 0/1 | localhost:5501 | primary | primary
$ pg_autoctl show state
Name | Node | Host:Port | LSN | Connection | Current State | Assigned State
------+-------+----------------+-----------+--------------+---------------------+--------------------
node1 | 1 | localhost:5501 | 0/40012F0 | read-write | primary | primary
node2 | 2 | localhost:5502 | 0/40012F0 | read-only | secondary | secondary
node3 | 3 | localhost:5503 | 0/40012F0 | read-only | secondary | secondary
pg_autoctl do
pg_autoctl do - Internal commands and internal QA tooling
The debug commands for pg_autoctl are only available when the environment variable PG_AUTOCTL_DEBUG is
set (to any value).
When testing pg_auto_failover, it is helpful to be able to play with the local nodes using the same
lower-level API as used by the pg_auto_failover Finite State Machine transitions. Some commands could be
useful in contexts other than pg_auto_failover development and QA work, so some documentation has been
made available.
pg_autoctl do tmux
pg_autoctl do tmux - Set of facilities to handle tmux interactive sessions
Synopsis
pg_autoctl do tmux provides the following commands:
pg_autoctl do tmux
+ compose Set of facilities to handle docker-compose sessions
script Produce a tmux script for a demo or a test case (debug only)
session Run a tmux session for a demo or a test case
stop Stop pg_autoctl processes that belong to a tmux session
wait Wait until a given node has been registered on the monitor
clean Clean-up a tmux session processes and root dir
pg_autoctl do tmux compose
config Produce a docker-compose configuration file for a demo
script Produce a tmux script for a demo or a test case (debug only)
session Run a tmux session for a demo or a test case
Description
An easy way to get started with pg_auto_failover in a localhost only formation with three nodes is to run
the following command:
$ PG_AUTOCTL_DEBUG=1 pg_autoctl do tmux session \
--root /tmp/pgaf \
--first-pgport 9000 \
--nodes 4 \
--layout tiled
This requires the command tmux to be available in your PATH. The pg_autoctl do tmux session commands
prepares a self-contained root directory where to create pg_auto_failover nodes and their configuration,
then prepares a tmux script, and then runs the script with a command such as:
/usr/local/bin/tmux -v start-server ; source-file /tmp/pgaf/script-9000.tmux
The tmux session contains a single tmux window multiple panes:
• one pane for the monitor
• one pane per Postgres nodes, here 4 of them
• one pane for running pg_autoctl watch
• one extra pane for an interactive shell.
Usually the first two commands to run in the interactive shell, once the formation is stable (one node is
primary, the other ones are all secondary), are the following:
$ pg_autoctl get formation settings
$ pg_autoctl perform failover
Using docker-compose to run a distributed system
The same idea can also be implemented with docker-compose to run the nodes, and still using tmux to have
three control panels this time:
• one pane for the docker-compose cumulative logs of all the nodes
• one pane for running pg_autoctl watch
• one extra pane for an interactive shell.
For this setup, you can use the following command:
PG_AUTOCTL_DEBUG=1 pg_autoctl do tmux compose session \
--root ./tmux/citus \
--first-pgport 5600 \
--nodes 3 \
--async-nodes 0 \
--node-priorities 50,50,0 \
--sync-standbys -1 \
--citus-workers 4 \
--citus-secondaries 0 \
--citus \
--layout even-vertical
The pg_autoctl do tmux compose session command also takes care of creating external docker volumes and
referencing them for each node in the docker-compose file.
pg_autoctl do tmux session
This command runs a tmux session for a demo or a test case.
usage: pg_autoctl do tmux session [option ...]
--root path where to create a cluster
--first-pgport first Postgres port to use (5500)
--nodes number of Postgres nodes to create (2)
--async-nodes number of async nodes within nodes (0)
--node-priorities list of nodes priorities (50)
--sync-standbys number-sync-standbys to set (0 or 1)
--skip-pg-hba use --skip-pg-hba when creating nodes
--citus start a Citus formation
--citus-workers number of Citus workers to create (2)
--citus-secondaries number of Citus secondaries to create (0)
--layout tmux layout to use (even-vertical)
--binpath path to the pg_autoctl binary (current binary path)
pg_autoctl do tmux compose session
This command runs a tmux session for a demo or a test case. It generates a docker-compose file and then
uses docker-compose to drive many nodes.
usage: pg_autoctl do tmux compose session [option ...]
--root path where to create a cluster
--first-pgport first Postgres port to use (5500)
--nodes number of Postgres nodes to create (2)
--async-nodes number of async nodes within nodes (0)
--node-priorities list of nodes priorities (50)
--sync-standbys number-sync-standbys to set (0 or 1)
--skip-pg-hba use --skip-pg-hba when creating nodes
--layout tmux layout to use (even-vertical)
--binpath path to the pg_autoctl binary (current binary path)
pg_autoctl do demo
pg_autoctl do demo - Use a demo application for pg_auto_failover
Synopsis
pg_autoctl do demo provides the following commands:
pg_autoctl do demo
run Run the pg_auto_failover demo application
uri Grab the application connection string from the monitor
ping Attempt to connect to the application URI
summary Display a summary of the previous demo app run
To run a demo, use pg_autoctl do demo run:
usage: pg_autoctl do demo run [option ...]
--monitor Postgres URI of the pg_auto_failover monitor
--formation Formation to use (default)
--group Group Id to failover (0)
--username PostgreSQL's username
--clients How many client processes to use (1)
--duration Duration of the demo app, in seconds (30)
--first-failover Timing of the first failover (10)
--failover-freq Seconds between subsequent failovers (45)
Description
The pg_autoctl debug tooling includes a demo application.
The demo prepare its Postgres schema on the target database, and then starts several clients (see
--clients) that concurrently connect to the target application URI and record the time it took to
establish the Postgres connection to the current read-write node, with information about the retry policy
metrics.
Example
$ pg_autoctl do demo run --monitor 'postgres://autoctl_node@localhost:5500/pg_auto_failover?sslmode=prefer' --clients 10
14:43:35 19660 INFO Using application connection string "postgres://localhost:5502,localhost:5503,localhost:5501/demo?target_session_attrs=read-write&sslmode=prefer"
14:43:35 19660 INFO Using Postgres user PGUSER "dim"
14:43:35 19660 INFO Preparing demo schema: drop schema if exists demo cascade
14:43:35 19660 WARN NOTICE: schema "demo" does not exist, skipping
14:43:35 19660 INFO Preparing demo schema: create schema demo
14:43:35 19660 INFO Preparing demo schema: create table demo.tracking(ts timestamptz default now(), client integer, loop integer, retries integer, us bigint, recovery bool)
14:43:36 19660 INFO Preparing demo schema: create table demo.client(client integer, pid integer, retry_sleep_ms integer, retry_cap_ms integer, failover_count integer)
14:43:36 19660 INFO Starting 10 concurrent clients as sub-processes
14:43:36 19675 INFO Failover client is started, will failover in 10s and every 45s after that
...
$ pg_autoctl do demo summary --monitor 'postgres://autoctl_node@localhost:5500/pg_auto_failover?sslmode=prefer' --clients 10
14:44:27 22789 INFO Using application connection string "postgres://localhost:5503,localhost:5501,localhost:5502/demo?target_session_attrs=read-write&sslmode=prefer"
14:44:27 22789 INFO Using Postgres user PGUSER "dim"
14:44:27 22789 INFO Summary for the demo app running with 10 clients for 30s
Client | Connections | Retries | Min Connect Time (ms) | max | p95 | p99
----------------------+-------------+---------+-----------------------+----------+---------+---------
Client 1 | 136 | 14 | 58.318 | 2601.165 | 244.443 | 261.809
Client 2 | 136 | 5 | 55.199 | 2514.968 | 242.362 | 259.282
Client 3 | 134 | 6 | 55.815 | 2974.247 | 241.740 | 262.908
Client 4 | 135 | 7 | 56.542 | 2970.922 | 238.995 | 251.177
Client 5 | 136 | 8 | 58.339 | 2758.106 | 238.720 | 252.439
Client 6 | 134 | 9 | 58.679 | 2813.653 | 244.696 | 254.674
Client 7 | 134 | 11 | 58.737 | 2795.974 | 243.202 | 253.745
Client 8 | 136 | 12 | 52.109 | 2354.952 | 242.664 | 254.233
Client 9 | 137 | 19 | 59.735 | 2628.496 | 235.668 | 253.582
Client 10 | 133 | 6 | 57.994 | 3060.489 | 242.156 | 256.085
All Clients Combined | 1351 | 97 | 52.109 | 3060.489 | 241.848 | 258.450
(11 rows)
Min Connect Time (ms) | max | freq | bar
-----------------------+----------+------+-----------------------------------------------
52.109 | 219.105 | 1093 | ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒
219.515 | 267.168 | 248 | ▒▒▒▒▒▒▒▒▒▒
2354.952 | 2354.952 | 1 |
2514.968 | 2514.968 | 1 |
2601.165 | 2628.496 | 2 |
2758.106 | 2813.653 | 3 |
2970.922 | 2974.247 | 2 |
3060.489 | 3060.489 | 1 |
(8 rows)
pg_autoctl do service restart
pg_autoctl do service restart - Run pg_autoctl sub-processes (services)
Synopsis
pg_autoctl do service restart provides the following commands:
pg_autoctl do service restart
postgres Restart the pg_autoctl postgres controller service
listener Restart the pg_autoctl monitor listener service
node-active Restart the pg_autoctl keeper node-active service
Description
It is possible to restart the pg_autoctl or the Postgres service without affecting the other running
service. Typically, to restart the pg_autoctl parts without impacting Postgres:
$ pg_autoctl do service restart node-active --pgdata node1
14:52:06 31223 INFO Sending the TERM signal to service "node-active" with pid 26626
14:52:06 31223 INFO Service "node-active" has been restarted with pid 31230
31230
The Postgres service has not been impacted by the restart of the pg_autoctl process.
pg_autoctl do show
pg_autoctl do show - Show some debug level information
Synopsis
The commands pg_autoctl create monitor and pg_autoctl create postgres both implement some level of
automated detection of the node network settings when the option --hostname is not used.
Adding to those commands, when a new node is registered to the monitor, other nodes also edit their
Postgres HBA rules to allow the new node to connect, unless the option --skip-pg-hba has been used.
The debug sub-commands for pg_autoctl do show can be used to see in details the network discovery done by
pg_autoctl.
pg_autoctl do show provides the following commands:
pg_autoctl do show
ipaddr Print this node's IP address information
cidr Print this node's CIDR information
lookup Print this node's DNS lookup information
hostname Print this node's default hostname
reverse Lookup given hostname and check reverse DNS setup
pg_autoctl do show ipaddr
Connects to an external IP address and uses getsockname(2) to retrieve the current address to which the
socket is bound.
The external IP address defaults to 8.8.8.8, the IP address of a Google provided public DNS server, or to
the monitor IP address or hostname in the context of pg_autoctl create postgres.
$ pg_autoctl do show ipaddr
16:42:40 62631 INFO ipaddr.c:107: Connecting to 8.8.8.8 (port 53)
192.168.1.156
pg_autoctl do show cidr
Connects to an external IP address in the same way as the previous command pg_autoctl do show ipaddr and
then matches the local socket name with the list of local network interfaces. When a match is found, uses
the netmask of the interface to compute the CIDR notation from the IP address.
The computed CIDR notation is then used in HBA rules.
$ pg_autoctl do show cidr
16:43:19 63319 INFO Connecting to 8.8.8.8 (port 53)
192.168.1.0/24
pg_autoctl do show hostname
Uses either its first (and only) argument or the result of gethostname(2) as the candidate hostname to
use in HBA rules, and then check that the hostname resolves to an IP address that belongs to one of the
machine network interfaces.
When the hostname forward-dns lookup resolves to an IP address that is local to the node where the
command is run, then a reverse-lookup from the IP address is made to see if it matches with the candidate
hostname.
$ pg_autoctl do show hostname
DESKTOP-IC01GOOS.europe.corp.microsoft.com
$ pg_autoctl -vv do show hostname 'postgres://autoctl_node@localhost:5500/pg_auto_failover'
13:45:00 93122 INFO cli_do_show.c:256: Using monitor hostname "localhost" and port 5500
13:45:00 93122 INFO ipaddr.c:107: Connecting to ::1 (port 5500)
13:45:00 93122 DEBUG cli_do_show.c:272: cli_show_hostname: ip ::1
13:45:00 93122 DEBUG cli_do_show.c:283: cli_show_hostname: host localhost
13:45:00 93122 DEBUG cli_do_show.c:294: cli_show_hostname: ip ::1
localhost
pg_autoctl do show lookup
Checks that the given argument is an hostname that resolves to a local IP address, that is an IP address
associated with a local network interface.
$ pg_autoctl do show lookup DESKTOP-IC01GOOS.europe.corp.microsoft.com
DESKTOP-IC01GOOS.europe.corp.microsoft.com: 192.168.1.156
pg_autoctl do show reverse
Implements the same DNS checks as Postgres HBA matching code: first does a forward DNS lookup of the
given hostname, and then a reverse-lookup from all the IP addresses obtained. Success is reached when at
least one of the IP addresses from the forward lookup resolves back to the given hostname (as the first
answer to the reverse DNS lookup).
$ pg_autoctl do show reverse DESKTOP-IC01GOOS.europe.corp.microsoft.com
16:44:49 64910 FATAL Failed to find an IP address for hostname "DESKTOP-IC01GOOS.europe.corp.microsoft.com" that matches hostname again in a reverse-DNS lookup.
16:44:49 64910 INFO Continuing with IP address "192.168.1.156"
$ pg_autoctl -vv do show reverse DESKTOP-IC01GOOS.europe.corp.microsoft.com
16:44:45 64832 DEBUG ipaddr.c:719: DESKTOP-IC01GOOS.europe.corp.microsoft.com has address 192.168.1.156
16:44:45 64832 DEBUG ipaddr.c:733: reverse lookup for "192.168.1.156" gives "desktop-ic01goos.europe.corp.microsoft.com" first
16:44:45 64832 DEBUG ipaddr.c:719: DESKTOP-IC01GOOS.europe.corp.microsoft.com has address 192.168.1.156
16:44:45 64832 DEBUG ipaddr.c:733: reverse lookup for "192.168.1.156" gives "desktop-ic01goos.europe.corp.microsoft.com" first
16:44:45 64832 DEBUG ipaddr.c:719: DESKTOP-IC01GOOS.europe.corp.microsoft.com has address 2a01:110:10:40c::2ad
16:44:45 64832 DEBUG ipaddr.c:728: Failed to resolve hostname from address "192.168.1.156": nodename nor servname provided, or not known
16:44:45 64832 DEBUG ipaddr.c:719: DESKTOP-IC01GOOS.europe.corp.microsoft.com has address 2a01:110:10:40c::2ad
16:44:45 64832 DEBUG ipaddr.c:728: Failed to resolve hostname from address "192.168.1.156": nodename nor servname provided, or not known
16:44:45 64832 DEBUG ipaddr.c:719: DESKTOP-IC01GOOS.europe.corp.microsoft.com has address 100.64.34.213
16:44:45 64832 DEBUG ipaddr.c:728: Failed to resolve hostname from address "192.168.1.156": nodename nor servname provided, or not known
16:44:45 64832 DEBUG ipaddr.c:719: DESKTOP-IC01GOOS.europe.corp.microsoft.com has address 100.64.34.213
16:44:45 64832 DEBUG ipaddr.c:728: Failed to resolve hostname from address "192.168.1.156": nodename nor servname provided, or not known
16:44:45 64832 FATAL cli_do_show.c:333: Failed to find an IP address for hostname "DESKTOP-IC01GOOS.europe.corp.microsoft.com" that matches hostname again in a reverse-DNS lookup.
16:44:45 64832 INFO cli_do_show.c:334: Continuing with IP address "192.168.1.156"
pg_autoctl do pgsetup
pg_autoctl do pgsetup - Manage a local Postgres setup
Synopsis
The main pg_autoctl commands implement low-level management tooling for a local Postgres instance. Some
of the low-level Postgres commands can be used as their own tool in some cases.
pg_autoctl do pgsetup provides the following commands:
pg_autoctl do pgsetup
pg_ctl Find a non-ambiguous pg_ctl program and Postgres version
discover Discover local PostgreSQL instance, if any
ready Return true is the local Postgres server is ready
wait Wait until the local Postgres server is ready
logs Outputs the Postgres startup logs
tune Compute and log some Postgres tuning options
pg_autoctl do pgsetup pg_ctl
In a similar way to which -a, this commands scans your PATH for pg_ctl commands. Then it runs the pg_ctl
--version command and parses the output to determine the version of Postgres that is available in the
path.
$ pg_autoctl do pgsetup pg_ctl --pgdata node1
16:49:18 69684 INFO Environment variable PG_CONFIG is set to "/Applications/Postgres.app//Contents/Versions/12/bin/pg_config"
16:49:18 69684 INFO `pg_autoctl create postgres` would use "/Applications/Postgres.app/Contents/Versions/12/bin/pg_ctl" for Postgres 12.3
16:49:18 69684 INFO `pg_autoctl create monitor` would use "/Applications/Postgres.app/Contents/Versions/12/bin/pg_ctl" for Postgres 12.3
pg_autoctl do pgsetup discover
Given a PGDATA or --pgdata option, the command discovers if a running Postgres service matches the
pg_autoctl setup, and prints the information that pg_autoctl typically needs when managing a Postgres
instance.
$ pg_autoctl do pgsetup discover --pgdata node1
pgdata: /Users/dim/dev/MS/pg_auto_failover/tmux/node1
pg_ctl: /Applications/Postgres.app/Contents/Versions/12/bin/pg_ctl
pg_version: 12.3
pghost: /tmp
pgport: 5501
proxyport: 0
pid: 21029
is in recovery: no
Control Version: 1201
Catalog Version: 201909212
System Identifier: 6942422768095393833
Latest checkpoint LSN: 0/4059C18
Postmaster status: ready
pg_autoctl do pgsetup ready
Similar to the pg_isready command, though uses the Postgres specifications found in the pg_autoctl node
setup.
$ pg_autoctl do pgsetup ready --pgdata node1
16:50:08 70582 INFO Postgres status is: "ready"
pg_autoctl do pgsetup wait
When pg_autoctl do pgsetup ready would return false because Postgres is not ready yet, this command
continues probing every second for 30 seconds, and exists as soon as Postgres is ready.
$ pg_autoctl do pgsetup wait --pgdata node1
16:50:22 70829 INFO Postgres is now serving PGDATA "/Users/dim/dev/MS/pg_auto_failover/tmux/node1" on port 5501 with pid 21029
16:50:22 70829 INFO Postgres status is: "ready"
pg_autoctl do pgsetup logs
Outputs the Postgres logs from the most recent log file in the PGDATA/log directory.
$ pg_autoctl do pgsetup logs --pgdata node1
16:50:39 71126 WARN Postgres logs from "/Users/dim/dev/MS/pg_auto_failover/tmux/node1/startup.log":
16:50:39 71126 INFO 2021-03-22 14:43:48.911 CET [21029] LOG: starting PostgreSQL 12.3 on x86_64-apple-darwin16.7.0, compiled by Apple LLVM version 8.1.0 (clang-802.0.42), 64-bit
16:50:39 71126 INFO 2021-03-22 14:43:48.913 CET [21029] LOG: listening on IPv6 address "::", port 5501
16:50:39 71126 INFO 2021-03-22 14:43:48.913 CET [21029] LOG: listening on IPv4 address "0.0.0.0", port 5501
16:50:39 71126 INFO 2021-03-22 14:43:48.913 CET [21029] LOG: listening on Unix socket "/tmp/.s.PGSQL.5501"
16:50:39 71126 INFO 2021-03-22 14:43:48.931 CET [21029] LOG: redirecting log output to logging collector process
16:50:39 71126 INFO 2021-03-22 14:43:48.931 CET [21029] HINT: Future log output will appear in directory "log".
16:50:39 71126 WARN Postgres logs from "/Users/dim/dev/MS/pg_auto_failover/tmux/node1/log/postgresql-2021-03-22_144348.log":
16:50:39 71126 INFO 2021-03-22 14:43:48.937 CET [21033] LOG: database system was shut down at 2021-03-22 14:43:46 CET
16:50:39 71126 INFO 2021-03-22 14:43:48.937 CET [21033] LOG: entering standby mode
16:50:39 71126 INFO 2021-03-22 14:43:48.942 CET [21033] LOG: consistent recovery state reached at 0/4022E88
16:50:39 71126 INFO 2021-03-22 14:43:48.942 CET [21033] LOG: invalid record length at 0/4022E88: wanted 24, got 0
16:50:39 71126 INFO 2021-03-22 14:43:48.946 CET [21029] LOG: database system is ready to accept read only connections
16:50:39 71126 INFO 2021-03-22 14:43:49.032 CET [21038] LOG: fetching timeline history file for timeline 4 from primary server
16:50:39 71126 INFO 2021-03-22 14:43:49.037 CET [21038] LOG: started streaming WAL from primary at 0/4000000 on timeline 3
16:50:39 71126 INFO 2021-03-22 14:43:49.046 CET [21038] LOG: replication terminated by primary server
16:50:39 71126 INFO 2021-03-22 14:43:49.046 CET [21038] DETAIL: End of WAL reached on timeline 3 at 0/4022E88.
16:50:39 71126 INFO 2021-03-22 14:43:49.047 CET [21033] LOG: new target timeline is 4
16:50:39 71126 INFO 2021-03-22 14:43:49.049 CET [21038] LOG: restarted WAL streaming at 0/4000000 on timeline 4
16:50:39 71126 INFO 2021-03-22 14:43:49.210 CET [21033] LOG: redo starts at 0/4022E88
16:50:39 71126 INFO 2021-03-22 14:52:06.692 CET [21029] LOG: received SIGHUP, reloading configuration files
16:50:39 71126 INFO 2021-03-22 14:52:06.906 CET [21029] LOG: received SIGHUP, reloading configuration files
16:50:39 71126 FATAL 2021-03-22 15:34:24.920 CET [21038] FATAL: terminating walreceiver due to timeout
16:50:39 71126 INFO 2021-03-22 15:34:24.973 CET [21033] LOG: invalid record length at 0/4059CC8: wanted 24, got 0
16:50:39 71126 INFO 2021-03-22 15:34:25.105 CET [35801] LOG: started streaming WAL from primary at 0/4000000 on timeline 4
16:50:39 71126 FATAL 2021-03-22 16:12:56.918 CET [35801] FATAL: terminating walreceiver due to timeout
16:50:39 71126 INFO 2021-03-22 16:12:57.086 CET [38741] LOG: started streaming WAL from primary at 0/4000000 on timeline 4
16:50:39 71126 FATAL 2021-03-22 16:23:39.349 CET [38741] FATAL: terminating walreceiver due to timeout
16:50:39 71126 INFO 2021-03-22 16:23:39.497 CET [41635] LOG: started streaming WAL from primary at 0/4000000 on timeline 4
pg_autoctl do pgsetup tune
Outputs the pg_autoctl automated tuning options. Depending on the number of CPU and amount of RAM
detected in the environment where it is run, pg_autoctl can adjust some very basic Postgres tuning knobs
to get started.
$ pg_autoctl do pgsetup tune --pgdata node1 -vv
13:25:25 77185 DEBUG pgtuning.c:85: Detected 12 CPUs and 16 GB total RAM on this server
13:25:25 77185 DEBUG pgtuning.c:225: Setting autovacuum_max_workers to 3
13:25:25 77185 DEBUG pgtuning.c:228: Setting shared_buffers to 4096 MB
13:25:25 77185 DEBUG pgtuning.c:231: Setting work_mem to 24 MB
13:25:25 77185 DEBUG pgtuning.c:235: Setting maintenance_work_mem to 512 MB
13:25:25 77185 DEBUG pgtuning.c:239: Setting effective_cache_size to 12 GB
# basic tuning computed by pg_auto_failover
track_functions = pl
shared_buffers = '4096 MB'
work_mem = '24 MB'
maintenance_work_mem = '512 MB'
effective_cache_size = '12 GB'
autovacuum_max_workers = 3
autovacuum_vacuum_scale_factor = 0.08
autovacuum_analyze_scale_factor = 0.02
The low-level API is made available through the following pg_autoctl do commands, only available in debug
environments:
pg_autoctl do
+ monitor Query a pg_auto_failover monitor
+ fsm Manually manage the keeper's state
+ primary Manage a PostgreSQL primary server
+ standby Manage a PostgreSQL standby server
+ show Show some debug level information
+ pgsetup Manage a local Postgres setup
+ pgctl Signal the pg_autoctl postgres service
+ service Run pg_autoctl sub-processes (services)
+ tmux Set of facilities to handle tmux interactive sessions
+ azure Manage a set of Azure resources for a pg_auto_failover demo
+ demo Use a demo application for pg_auto_failover
pg_autoctl do monitor
+ get Get information from the monitor
register Register the current node with the monitor
active Call in the pg_auto_failover Node Active protocol
version Check that monitor version is 1.5.0.1; alter extension update if not
parse-notification parse a raw notification message
pg_autoctl do monitor get
primary Get the primary node from pg_auto_failover in given formation/group
others Get the other nodes from the pg_auto_failover group of hostname/port
coordinator Get the coordinator node from the pg_auto_failover formation
pg_autoctl do fsm
init Initialize the keeper's state on-disk
state Read the keeper's state from disk and display it
list List reachable FSM states from current state
gv Output the FSM as a .gv program suitable for graphviz/dot
assign Assign a new goal state to the keeper
step Make a state transition if instructed by the monitor
+ nodes Manually manage the keeper's nodes list
pg_autoctl do fsm nodes
get Get the list of nodes from file (see --disable-monitor)
set Set the list of nodes to file (see --disable-monitor)
pg_autoctl do primary
+ slot Manage replication slot on the primary server
+ adduser Create users on primary
defaults Add default settings to postgresql.conf
identify Run the IDENTIFY_SYSTEM replication command on given host
pg_autoctl do primary slot
create Create a replication slot on the primary server
drop Drop a replication slot on the primary server
pg_autoctl do primary adduser
monitor add a local user for queries from the monitor
replica add a local user with replication privileges
pg_autoctl do standby
init Initialize the standby server using pg_basebackup
rewind Rewind a demoted primary server using pg_rewind
promote Promote a standby server to become writable
pg_autoctl do show
ipaddr Print this node's IP address information
cidr Print this node's CIDR information
lookup Print this node's DNS lookup information
hostname Print this node's default hostname
reverse Lookup given hostname and check reverse DNS setup
pg_autoctl do pgsetup
pg_ctl Find a non-ambiguous pg_ctl program and Postgres version
discover Discover local PostgreSQL instance, if any
ready Return true is the local Postgres server is ready
wait Wait until the local Postgres server is ready
logs Outputs the Postgres startup logs
tune Compute and log some Postgres tuning options
pg_autoctl do pgctl
on Signal pg_autoctl postgres service to ensure Postgres is running
off Signal pg_autoctl postgres service to ensure Postgres is stopped
pg_autoctl do service
+ getpid Get the pid of pg_autoctl sub-processes (services)
+ restart Restart pg_autoctl sub-processes (services)
pgcontroller pg_autoctl supervised postgres controller
postgres pg_autoctl service that start/stop postgres when asked
listener pg_autoctl service that listens to the monitor notifications
node-active pg_autoctl service that implements the node active protocol
pg_autoctl do service getpid
postgres Get the pid of the pg_autoctl postgres controller service
listener Get the pid of the pg_autoctl monitor listener service
node-active Get the pid of the pg_autoctl keeper node-active service
pg_autoctl do service restart
postgres Restart the pg_autoctl postgres controller service
listener Restart the pg_autoctl monitor listener service
node-active Restart the pg_autoctl keeper node-active service
pg_autoctl do tmux
script Produce a tmux script for a demo or a test case (debug only)
session Run a tmux session for a demo or a test case
stop Stop pg_autoctl processes that belong to a tmux session
wait Wait until a given node has been registered on the monitor
clean Clean-up a tmux session processes and root dir
pg_autoctl do azure
+ provision provision azure resources for a pg_auto_failover demo
+ tmux Run a tmux session with an Azure setup for QA/testing
+ show show azure resources for a pg_auto_failover demo
deploy Deploy a pg_autoctl VMs, given by name
create Create an azure QA environment
drop Drop an azure QA environment: resource group, network, VMs
ls List resources in a given azure region
ssh Runs ssh -l ha-admin <public ip address> for a given VM name
sync Rsync pg_auto_failover sources on all the target region VMs
pg_autoctl do azure provision
region Provision an azure region: resource group, network, VMs
nodes Provision our pre-created VM with pg_autoctl Postgres nodes
pg_autoctl do azure tmux
session Create or attach a tmux session for the created Azure VMs
kill Kill an existing tmux session for Azure VMs
pg_autoctl do azure show
ips Show public and private IP addresses for selected VMs
state Connect to the monitor node to show the current state
pg_autoctl do demo
run Run the pg_auto_failover demo application
uri Grab the application connection string from the monitor
ping Attempt to connect to the application URI
summary Display a summary of the previous demo app run
pg_autoctl run
pg_autoctl run - Run the pg_autoctl service (monitor or keeper)
Synopsis
This commands starts the processes needed to run a monitor node or a keeper node, depending on the
configuration file that belongs to the --pgdata option or PGDATA environment variable.
usage: pg_autoctl run [ --pgdata --name --hostname --pgport ]
--pgdata path to data directory
--name pg_auto_failover node name
--hostname hostname used to connect from other nodes
--pgport PostgreSQL's port number
Description
When registering Postgres nodes to the pg_auto_failover monitor using the pg_autoctl create postgres
command, the nodes are registered with metadata: the node name, hostname and Postgres port.
The node name is used mostly in the logs and pg_autoctl show state commands and helps human
administrators of the formation.
The node hostname and pgport are used by other nodes, including the pg_auto_failover monitor, to open a
Postgres connection.
Both the node name and the node hostname and port can be changed after the node registration by using
either this command (pg_autoctl run) or the pg_autoctl config set command.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--name Node name used on the monitor to refer to this node. The hostname is a technical information, and
given Postgres requirements on the HBA setup and DNS resolution (both forward and reverse
lookups), IP addresses are often used for the hostname.
The --name option allows using a user-friendly name for your Postgres nodes.
--hostname
Hostname or IP address (both v4 and v6 are supported) to use from any other node to connect to
this node.
When not provided, a default value is computed by running the following algorithm.
1. We get this machine's "public IP" by opening a connection to the given monitor hostname or
IP address. Then we get TCP/IP client address that has been used to make that connection.
2. We then do a reverse DNS lookup on the IP address found in the previous step to fetch a
hostname for our local machine.
3. If the reverse DNS lookup is successful , then pg_autoctl does a forward DNS lookup of that
hostname.
When the forward DNS lookup response in step 3. is an IP address found in one of our local network
interfaces, then pg_autoctl uses the hostname found in step 2. as the default --hostname.
Otherwise it uses the IP address found in step 1.
You may use the --hostname command line option to bypass the whole DNS lookup based process and
force the local node name to a fixed value.
--pgport
Postgres port to use, defaults to 5432.
pg_autoctl watch
pg_autoctl watch - Display an auto-updating dashboard
Synopsis
This command outputs the events that the pg_auto_failover events records about state changes of the
pg_auto_failover nodes managed by the monitor:
usage: pg_autoctl watch [ --pgdata --formation --group ]
--pgdata path to data directory
--monitor show the monitor uri
--formation formation to query, defaults to 'default'
--group group to query formation, defaults to all
--json output data in the JSON format
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--monitor
Postgres URI used to connect to the monitor. Must use the autoctl_node username and target the
pg_auto_failover database name. It is possible to show the Postgres URI from the monitor node
using the command pg_autoctl show uri.
--formation
List the events recorded for nodes in the given formation. Defaults to default.
--group
Limit output to a single group in the formation. Default to including all groups registered in the
target formation.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Description
The pg_autoctl watch output is divided in 3 sections.
The first section is a single header line which includes the name of the currently selected formation,
the formation replication setting Number Sync Standbys, and then in the right most position the current
time.
The second section displays one line per node, and each line contains a list of columns that describe the
current state for the node. This list can includes the following columns, and which columns are part of
the output depends on the terminal window size. This choice is dynamic and changes if your terminal
window size changes:
• Name
Name of the node.
• Node, or Id
Node information. When the formation has a single group (group zero), then this column only
contains the nodeId.
Only Citus formations allow several groups. When using a Citus formation the Node column
contains the groupId and the nodeId, separated by a colon, such as 0:1 for the first coordinator
node.
• Last Report, or Report
Time interval between now and the last known time when a node has reported to the monitor, using
the node_active protocol.
This value is expected to stay under 2s or abouts, and is known to increment when either the
pg_autoctl run service is not running, or when there is a network split.
• Last Check, or Check
Time interval between now and the last known time when the monitor could connect to a node's
Postgres instance, via its health check mechanism.
This value is known to increment when either the Postgres service is not running on the target
node, when there is a network split, or when the internal machinery (the health check worker
background process) implements jitter.
• Host:Port
Hostname and port number used to connect to the node.
• TLI: LSN
Timeline identifier (TLI) and Postgres Log Sequence Number (LSN).
The LSN is the current position in the Postgres WAL stream. This is a hexadecimal number. See
pg_lsn for more information.
The current timeline is incremented each time a failover happens, or when doing Point In Time
Recovery. A node can only reach the secondary state when it is on the same timeline as its
primary node.
• Connection
This output field contains two bits of information. First, the Postgres connection type that the
node provides, either read-write or read-only. Then the mark ! is added when the monitor has
failed to connect to this node, and ? when the monitor didn't connect to the node yet.
• Reported State
The current FSM state as reported to the monitor by the pg_autoctl process running on the
Postgres node.
• Assigned State
The assigned FSM state on the monitor. When the assigned state is not the same as the reported
start, then the pg_autoctl process running on the Postgres node might have not retrieved the
assigned state yet, or might still be implementing the FSM transition from the current state to
the assigned state.
The third and last section lists the most recent events that the monitor has registered, the more recent
event is found at the bottom of the screen.
To quit the command hit either the F1 key or the q key.
pg_autoctl stop
pg_autoctl stop - signal the pg_autoctl service for it to stop
Synopsis
This commands stops the processes needed to run a monitor node or a keeper node, depending on the
configuration file that belongs to the --pgdata option or PGDATA environment variable.
usage: pg_autoctl stop [ --pgdata --fast --immediate ]
--pgdata path to data directory
--fast fast shutdown mode for the keeper
--immediate immediate shutdown mode for the keeper
Description
The pg_autoctl stop commands finds the PID of the running service for the given --pgdata, and if the
process is still running, sends a SIGTERM signal to the process.
When pg_autoclt receives a shutdown signal a shutdown sequence is triggered. Depending on the signal
received, an operation that has been started (such as a state transition) is either run to completion,
stopped as the next opportunity, or stopped immediately even when in the middle of the transition.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
--fast Fast Shutdown mode for pg_autoctl. Sends the SIGINT signal to the running service, which is the
same as using C-c on an interactive process running as a foreground shell job.
--immediate
Immediate Shutdown mode for pg_autoctl. Sends the SIGQUIT signal to the running service.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node, can be used instead of the --monitor option.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
pg_autoctl reload
pg_autoctl reload - signal the pg_autoctl for it to reload its configuration
Synopsis
This commands signals a running pg_autoctl process to reload its configuration from disk, and also signal
the managed Postgres service to reload its configuration.
usage: pg_autoctl reload [ --pgdata ] [ --json ]
--pgdata path to data directory
Description
The pg_autoctl reload commands finds the PID of the running service for the given --pgdata, and if the
process is still running, sends a SIGHUP signal to the process.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
pg_autoctl status
pg_autoctl status - Display the current status of the pg_autoctl service
Synopsis
This commands outputs the current process status for the pg_autoctl service running for the given
--pgdata location.
usage: pg_autoctl status [ --pgdata ] [ --json ]
--pgdata path to data directory
--json output data in the JSON format
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
--json Output a JSON formatted data instead of a table formatted list.
Environment
PGDATA
Postgres directory location. Can be used instead of the --pgdata option.
PG_AUTOCTL_MONITOR
Postgres URI to connect to the monitor node.
XDG_CONFIG_HOME
The pg_autoctl command stores its configuration files in the standard place XDG_CONFIG_HOME. See the
XDG Base Directory Specification.
XDG_DATA_HOME
The pg_autoctl command stores its internal states files in the standard place XDG_DATA_HOME, which
defaults to ~/.local/share. See the XDG Base Directory Specification.
Example
$ pg_autoctl status --pgdata node1
11:26:30 27248 INFO pg_autoctl is running with pid 26618
11:26:30 27248 INFO Postgres is serving PGDATA "/Users/dim/dev/MS/pg_auto_failover/tmux/node1" on port 5501 with pid 26725
$ pg_autoctl status --pgdata node1 --json
11:26:37 27385 INFO pg_autoctl is running with pid 26618
11:26:37 27385 INFO Postgres is serving PGDATA "/Users/dim/dev/MS/pg_auto_failover/tmux/node1" on port 5501 with pid 26725
{
"postgres": {
"pgdata": "\/Users\/dim\/dev\/MS\/pg_auto_failover\/tmux\/node1",
"pg_ctl": "\/Applications\/Postgres.app\/Contents\/Versions\/12\/bin\/pg_ctl",
"version": "12.3",
"host": "\/tmp",
"port": 5501,
"proxyport": 0,
"pid": 26725,
"in_recovery": false,
"control": {
"version": 0,
"catalog_version": 0,
"system_identifier": "0"
},
"postmaster": {
"status": "ready"
}
},
"pg_autoctl": {
"pid": 26618,
"status": "running",
"pgdata": "\/Users\/dim\/dev\/MS\/pg_auto_failover\/tmux\/node1",
"version": "1.5.0",
"semId": 196609,
"services": [
{
"name": "postgres",
"pid": 26625,
"status": "running",
"version": "1.5.0",
"pgautofailover": "1.5.0.1"
},
{
"name": "node-active",
"pid": 26626,
"status": "running",
"version": "1.5.0",
"pgautofailover": "1.5.0.1"
}
]
}
}
pg_autoctl activate
pg_autoctl activate - Activate a Citus worker from the Citus coordinator
Synopsis
This command calls the Citus “activation” API so that a node can be used to host shards for your
reference and distributed tables.
usage: pg_autoctl activate [ --pgdata ]
--pgdata path to data directory
Description
When creating a Citus worker, pg_autoctl create worker automatically activates the worker node to the
coordinator. You only need this command when something unexpected have happened and you want to manually
make sure the worker node has been activated at the Citus coordinator level.
Starting with Citus 10 it is also possible to activate the coordinator itself as a node with shard
placement. Use pg_autoctl activate on your Citus coordinator node manually to use that feature.
When the Citus coordinator is activated, an extra step is then needed for it to host shards of
distributed tables. If you want your coordinator to have shards, then have a look at the Citus API
citus_set_node_property to set the shouldhaveshards property to true.
Options
--pgdata
Location of the Postgres node being managed locally. Defaults to the environment variable PGDATA.
Use --monitor to connect to a monitor from anywhere, rather than the monitor URI used by a local
Postgres node managed with pg_autoctl.
CONFIGURING PG_AUTO_FAILOVER
Several defaults settings of pg_auto_failover can be reviewed and changed depending on the trade-offs you
want to implement in your own production setup. The settings that you can change will have an impact of
the following operations:
• Deciding when to promote the secondary
pg_auto_failover decides to implement a failover to the secondary node when it detects that the
primary node is unhealthy. Changing the following settings will have an impact on when the
pg_auto_failover monitor decides to promote the secondary PostgreSQL node:
pgautofailover.health_check_max_retries
pgautofailover.health_check_period
pgautofailover.health_check_retry_delay
pgautofailover.health_check_timeout
pgautofailover.node_considered_unhealthy_timeout
• Time taken to promote the secondary
At secondary promotion time, pg_auto_failover waits for the following timeout to make sure that all
pending writes on the primary server made it to the secondary at shutdown time, thus preventing data
loss.:
pgautofailover.primary_demote_timeout
• Preventing promotion of the secondary
pg_auto_failover implements a trade-off where data availability trumps service availability. When
the primary node of a PostgreSQL service is detected unhealthy, the secondary is only promoted if it
was known to be eligible at the moment when the primary is lost.
In the case when synchronous replication was in use at the moment when the primary node is lost,
then we know we can switch to the secondary safely, and the wal lag is 0 in that case.
In the case when the secondary server had been detected unhealthy before, then the pg_auto_failover
monitor switches it from the state SECONDARY to the state CATCHING-UP and promotion is prevented
then.
The following setting allows to still promote the secondary, allowing for a window of data loss:
pgautofailover.promote_wal_log_threshold
pg_auto_failover Monitor
The configuration for the behavior of the monitor happens in the PostgreSQL database where the extension
has been deployed:
pg_auto_failover=> select name, setting, unit, short_desc from pg_settings where name ~ 'pgautofailover.';
-[ RECORD 1 ]----------------------------------------------------------------------------------------------------
name | pgautofailover.enable_sync_wal_log_threshold
setting | 16777216
unit |
short_desc | Don't enable synchronous replication until secondary xlog is within this many bytes of the primary's
-[ RECORD 2 ]----------------------------------------------------------------------------------------------------
name | pgautofailover.health_check_max_retries
setting | 2
unit |
short_desc | Maximum number of re-tries before marking a node as failed.
-[ RECORD 3 ]----------------------------------------------------------------------------------------------------
name | pgautofailover.health_check_period
setting | 5000
unit | ms
short_desc | Duration between each check (in milliseconds).
-[ RECORD 4 ]----------------------------------------------------------------------------------------------------
name | pgautofailover.health_check_retry_delay
setting | 2000
unit | ms
short_desc | Delay between consecutive retries.
-[ RECORD 5 ]----------------------------------------------------------------------------------------------------
name | pgautofailover.health_check_timeout
setting | 5000
unit | ms
short_desc | Connect timeout (in milliseconds).
-[ RECORD 6 ]----------------------------------------------------------------------------------------------------
name | pgautofailover.node_considered_unhealthy_timeout
setting | 20000
unit | ms
short_desc | Mark node unhealthy if last ping was over this long ago
-[ RECORD 7 ]----------------------------------------------------------------------------------------------------
name | pgautofailover.primary_demote_timeout
setting | 30000
unit | ms
short_desc | Give the primary this long to drain before promoting the secondary
-[ RECORD 8 ]----------------------------------------------------------------------------------------------------
name | pgautofailover.promote_wal_log_threshold
setting | 16777216
unit |
short_desc | Don't promote secondary unless xlog is with this many bytes of the master
-[ RECORD 9 ]----------------------------------------------------------------------------------------------------
name | pgautofailover.startup_grace_period
setting | 10000
unit | ms
short_desc | Wait for at least this much time after startup before initiating a failover.
You can edit the parameters as usual with PostgreSQL, either in the postgresql.conf file or using ALTER
DATABASE pg_auto_failover SET parameter = value; commands, then issuing a reload.
pg_auto_failover Keeper Service
For an introduction to the pg_autoctl commands relevant to the pg_auto_failover Keeper configuration,
please see pg_autoctl config.
An example configuration file looks like the following:
[pg_autoctl]
role = keeper
monitor = postgres://autoctl_node@192.168.1.34:6000/pg_auto_failover
formation = default
group = 0
hostname = node1.db
nodekind = standalone
[postgresql]
pgdata = /data/pgsql/
pg_ctl = /usr/pgsql-10/bin/pg_ctl
dbname = postgres
host = /tmp
port = 5000
[replication]
slot = pgautofailover_standby
maximum_backup_rate = 100M
backup_directory = /data/backup/node1.db
[timeout]
network_partition_timeout = 20
postgresql_restart_failure_timeout = 20
postgresql_restart_failure_max_retries = 3
To output, edit and check entries of the configuration, the following commands are provided:
pg_autoctl config check [--pgdata <pgdata>]
pg_autoctl config get [--pgdata <pgdata>] section.option
pg_autoctl config set [--pgdata <pgdata>] section.option value
The [postgresql] section is discovered automatically by the pg_autoctl command and is not intended to be
changed manually.
pg_autoctl.monitor
PostgreSQL service URL of the pg_auto_failover monitor, as given in the output of the pg_autoctl show uri
command.
pg_autoctl.formation
A single pg_auto_failover monitor may handle several postgres formations. The default formation name
default is usually fine.
pg_autoctl.group
This information is retrieved by the pg_auto_failover keeper when registering a node to the monitor, and
should not be changed afterwards. Use at your own risk.
pg_autoctl.hostname
Node hostname used by all the other nodes in the cluster to contact this node. In particular, if this
node is a primary then its standby uses that address to setup streaming replication.
replication.slot
Name of the PostgreSQL replication slot used in the streaming replication setup automatically deployed by
pg_auto_failover. Replication slots can't be renamed in PostgreSQL.
replication.maximum_backup_rate
When pg_auto_failover (re-)builds a standby node using the pg_basebackup command, this parameter is given
to pg_basebackup to throttle the network bandwidth used. Defaults to 100Mbps.
replication.backup_directory
When pg_auto_failover (re-)builds a standby node using the pg_basebackup command, this parameter is the
target directory where to copy the bits from the primary server. When the copy has been successful, then
the directory is renamed to postgresql.pgdata.
The default value is computed from ${PGDATA}/../backup/${hostname} and can be set to any value of your
preference. Remember that the directory renaming is an atomic operation only when both the source and the
target of the copy are in the same filesystem, at least in Unix systems.
timeout
This section allows to setup the behavior of the pg_auto_failover keeper in interesting scenarios.
timeout.network_partition_timeout
Timeout in seconds before we consider failure to communicate with other nodes indicates a network
partition. This check is only done on a PRIMARY server, so other nodes mean both the monitor and the
standby.
When a PRIMARY node is detected to be on the losing side of a network partition, the pg_auto_failover
keeper enters the DEMOTE state and stops the PostgreSQL instance in order to protect against split brain
situations.
The default is 20s.
timeout.postgresql_restart_failure_timeout
timeout.postgresql_restart_failure_max_retries
When PostgreSQL is not running, the first thing the pg_auto_failover keeper does is try to restart it. In
case of a transient failure (e.g. file system is full, or other dynamic OS resource constraint), the best
course of action is to try again for a little while before reaching out to the monitor and ask for a
failover.
The pg_auto_failover keeper tries to restart PostgreSQL timeout.postgresql_restart_failure_max_retries
times in a row (default 3) or up to timeout.postgresql_restart_failure_timeout (defaults 20s) since it
detected that PostgreSQL is not running, whichever comes first.
OPERATING PG_AUTO_FAILOVER
This section is not yet complete. Please contact us with any questions.
Deployment
pg_auto_failover is a general purpose tool for setting up PostgreSQL replication in order to implement
High Availability of the PostgreSQL service.
Provisioning
It is also possible to register pre-existing PostgreSQL instances with a pg_auto_failover monitor. The
pg_autoctl create command honors the PGDATA environment variable, and checks whether PostgreSQL is
already running. If Postgres is detected, the new node is registered in SINGLE mode, bypassing the
monitor's role assignment policy.
Postgres configuration management
The pg_autoctl create postgres command edits the default Postgres configuration file (postgresql.conf) to
include pg_auto_failover settings.
The include directive is placed on the top of the postgresql.conf file in a way that you may override any
setting by editing it later in the file.
Unless using the --skip-pg-hba option then pg_autoctl edits a minimal set of HBA rules for you, in order
for the pg_auto_failover nodes to be able to connect to each other. The HBA rules that are needed for
your application to connect to your Postgres nodes still need to be added. As pg_autoctl knows nothing
about your applications, then you are responsible for editing the HBA file.
Upgrading pg_auto_failover, from versions 1.4 onward
When upgrading a pg_auto_failover setup, the procedure is different on the monitor and on the Postgres
nodes:
• on the monitor, the internal pg_auto_failover database schema might have changed and needs to be
upgraded to its new definition, porting the existing data over. The pg_auto_failover database
contains the registration of every node in the system and their current state.
It is not possible to trigger a failover during the monitor update. Postgres operations on the
Postgres nodes continue normally.
During the restart of the monitor, the other nodes might have trouble connecting to the monitor.
The pg_autoctl command is designed to retry connecting to the monitor and handle errors
gracefully.
• on the Postgres nodes, the pg_autoctl command connects to the monitor every once in a while (every
second by default), and then calls the node_active protocol, a stored procedure in the monitor
databases.
The pg_autoctl also verifies at each connection to the monitor that it's running the expected
version of the extension. When that's not the case, the "node-active" sub-process quits, to be
restarted with the possibly new version of the pg_autoctl binary found on-disk.
As a result, here is the standard upgrade plan for pg_auto_failover:
1. Upgrade the pg_auto_failover package on the all the nodes, monitor included.
When using a debian based OS, this looks like the following command when from 1.4 to 1.5:
sudo apt-get remove pg-auto-failover-cli-1.4 postgresql-11-auto-failover-1.4
sudo apt-get install -q -y pg-auto-failover-cli-1.5 postgresql-11-auto-failover-1.5
2. Restart the pgautofailover service on the monitor.
When using the systemd integration, all we need to do is:
sudo systemctl restart pgautofailover
Then we may use the following commands to make sure that the service is running as expected:
sudo systemctl status pgautofailover
sudo journalctl -u pgautofailover
At this point it is expected that the pg_autoctl logs show that an upgrade has been performed
by using the ALTER EXTENSION pgautofailover UPDATE TO ... command. The monitor is ready with
the new version of pg_auto_failover.
When the Postgres nodes pg_autoctl process connects to the new monitor version, the check for version
compatibility fails, and the "node-active" sub-process exits. The main pg_autoctl process supervisor then
restart the "node-active" sub-process from its on-disk binary executable file, which has been upgraded to
the new version. That's why we first install the new packages for pg_auto_failover on every node, and
only then restart the monitor.
IMPORTANT:
Before upgrading the monitor, which is a simple restart of the pg_autoctl process, it is important
that the OS packages for pgautofailover be updated on all the Postgres nodes.
When that's not the case, pg_autoctl on the Postgres nodes will still detect a version mismatch with
the monitor extension, and the "node-active" sub-process will exit. And when restarted automatically,
the same version of the local pg_autoctl binary executable is found on-disk, leading to the same
version mismatch with the monitor extension.
After restarting the "node-active" process 5 times, pg_autoctl quits retrying and stops. This includes
stopping the Postgres service too, and a service downtime might then occur.
And when the upgrade is done we can use pg_autoctl show state on the monitor to see that eveything is as
expected.
Upgrading from previous pg_auto_failover versions
The new upgrade procedure described in the previous section is part of pg_auto_failover since version
1.4. When upgrading from a previous version of pg_auto_failover, up to and including version 1.3, then
all the pg_autoctl processes have to be restarted fully.
To prevent triggering a failover during the upgrade, it's best to put your secondary nodes in
maintenance. The procedure then looks like the following:
1. Enable maintenance on your secondary node(s):
pg_autoctl enable maintenance
2. Upgrade the OS packages for pg_auto_failover on every node, as per previous section.
3. Restart the monitor to upgrade it to the new pg_auto_failover version:
When using the systemd integration, all we need to do is:
sudo systemctl restart pgautofailover
Then we may use the following commands to make sure that the service is running as expected:
sudo systemctl status pgautofailover
sudo journalctl -u pgautofailover
At this point it is expected that the pg_autoctl logs show that an upgrade has been performed
by using the ALTER EXTENSION pgautofailover UPDATE TO ... command. The monitor is ready with
the new version of pg_auto_failover.
4. Restart pg_autoctl on all Postgres nodes on the cluster.
When using the systemd integration, all we need to do is:
sudo systemctl restart pgautofailover
As in the previous point in this list, make sure the service is now running as expected.
5. Disable maintenance on your secondary nodes(s):
pg_autoctl disable maintenance
Extension dependencies when upgrading the monitor
Since version 1.4.0 the pgautofailover extension requires the Postgres contrib extension btree_gist. The
pg_autoctl command arranges for the creation of this dependency, and has been buggy in some releases.
As a result, you might have trouble upgrade the pg_auto_failover monitor to a recent version. It is
possible to fix the error by connecting to the monitor Postgres database and running the create extension
command manually:
# create extension btree_gist;
Cluster Management and Operations
It is possible to operate pg_auto_failover formations and groups directly from the monitor. All that is
needed is an access to the monitor Postgres database as a client, such as psql. It's also possible to add
those management SQL function calls in your own ops application if you have one.
For security reasons, the autoctl_node is not allowed to perform maintenance operations. This user is
limited to what pg_autoctl needs. You can either create a specific user and authentication rule to
expose for management, or edit the default HBA rules for the autoctl user. In the following examples
we're directly connecting as the autoctl role.
The main operations with pg_auto_failover are node maintenance and manual failover, also known as a
controlled switchover.
Maintenance of a secondary node
It is possible to put a secondary node in any group in a MAINTENANCE state, so that the Postgres server
is not doing synchronous replication anymore and can be taken down for maintenance purposes, such as
security kernel upgrades or the like.
The command line tool pg_autoctl exposes an API to schedule maintenance operations on the current node,
which must be a secondary node at the moment when maintenance is requested.
Here's an example of using the maintenance commands on a secondary node, including the output. Of course,
when you try that on your own nodes, dates and PID information might differ:
$ pg_autoctl enable maintenance
17:49:19 14377 INFO Listening monitor notifications about state changes in formation "default" and group 0
17:49:19 14377 INFO Following table displays times when notifications are received
Time | ID | Host | Port | Current State | Assigned State
---------+-----+-----------+--------+---------------------+--------------------
17:49:19 | 1 | localhost | 5001 | primary | wait_primary
17:49:19 | 2 | localhost | 5002 | secondary | wait_maintenance
17:49:19 | 2 | localhost | 5002 | wait_maintenance | wait_maintenance
17:49:20 | 1 | localhost | 5001 | wait_primary | wait_primary
17:49:20 | 2 | localhost | 5002 | wait_maintenance | maintenance
17:49:20 | 2 | localhost | 5002 | maintenance | maintenance
The command listens to the state changes in the current node's formation and group on the monitor and
displays those changes as it receives them. The operation is done when the node has reached the
maintenance state.
It is now possible to disable maintenance to allow pg_autoctl to manage this standby node again:
$ pg_autoctl disable maintenance
17:49:26 14437 INFO Listening monitor notifications about state changes in formation "default" and group 0
17:49:26 14437 INFO Following table displays times when notifications are received
Time | ID | Host | Port | Current State | Assigned State
---------+-----+-----------+--------+---------------------+--------------------
17:49:27 | 2 | localhost | 5002 | maintenance | catchingup
17:49:27 | 2 | localhost | 5002 | catchingup | catchingup
17:49:28 | 2 | localhost | 5002 | catchingup | secondary
17:49:28 | 1 | localhost | 5001 | wait_primary | primary
17:49:28 | 2 | localhost | 5002 | secondary | secondary
17:49:29 | 1 | localhost | 5001 | primary | primary
When a standby node is in maintenance, the monitor sets the primary node replication to WAIT_PRIMARY: in
this role, the PostgreSQL streaming replication is now asynchronous and the standby PostgreSQL server may
be stopped, rebooted, etc.
Maintenance of a primary node
A primary node must be available at all times in any formation and group in pg_auto_failover, that is the
invariant provided by the whole solution. With that in mind, the only way to allow a primary node to go
to a maintenance mode is to first failover and promote the secondary node.
The same command pg_autoctl enable maintenance implements that operation when run on a primary node with
the option --allow-failover. Here is an example of such an operation:
$ pg_autoctl enable maintenance
11:53:03 50526 WARN Enabling maintenance on a primary causes a failover
11:53:03 50526 FATAL Please use --allow-failover to allow the command proceed
As we can see the option allow-failover is mandatory. In the next example we use it:
$ pg_autoctl enable maintenance --allow-failover
13:13:42 1614 INFO Listening monitor notifications about state changes in formation "default" and group 0
13:13:42 1614 INFO Following table displays times when notifications are received
Time | ID | Host | Port | Current State | Assigned State
---------+-----+-----------+--------+---------------------+--------------------
13:13:43 | 2 | localhost | 5002 | primary | prepare_maintenance
13:13:43 | 1 | localhost | 5001 | secondary | prepare_promotion
13:13:43 | 1 | localhost | 5001 | prepare_promotion | prepare_promotion
13:13:43 | 2 | localhost | 5002 | prepare_maintenance | prepare_maintenance
13:13:44 | 1 | localhost | 5001 | prepare_promotion | stop_replication
13:13:45 | 1 | localhost | 5001 | stop_replication | stop_replication
13:13:46 | 1 | localhost | 5001 | stop_replication | wait_primary
13:13:46 | 2 | localhost | 5002 | prepare_maintenance | maintenance
13:13:46 | 1 | localhost | 5001 | wait_primary | wait_primary
13:13:47 | 2 | localhost | 5002 | maintenance | maintenance
When the operation is done we can have the old primary re-join the group, this time as a secondary:
$ pg_autoctl disable maintenance
13:14:46 1985 INFO Listening monitor notifications about state changes in formation "default" and group 0
13:14:46 1985 INFO Following table displays times when notifications are received
Time | ID | Host | Port | Current State | Assigned State
---------+-----+-----------+--------+---------------------+--------------------
13:14:47 | 2 | localhost | 5002 | maintenance | catchingup
13:14:47 | 2 | localhost | 5002 | catchingup | catchingup
13:14:52 | 2 | localhost | 5002 | catchingup | secondary
13:14:52 | 1 | localhost | 5001 | wait_primary | primary
13:14:52 | 2 | localhost | 5002 | secondary | secondary
13:14:53 | 1 | localhost | 5001 | primary | primary
Triggering a failover
It is possible to trigger a manual failover, or a switchover, using the command pg_autoctl perform
failover. Here's an example of what happens when running the command:
$ pg_autoctl perform failover
11:58:00 53224 INFO Listening monitor notifications about state changes in formation "default" and group 0
11:58:00 53224 INFO Following table displays times when notifications are received
Time | ID | Host | Port | Current State | Assigned State
---------+-----+-----------+--------+--------------------+-------------------
11:58:01 | 1 | localhost | 5001 | primary | draining
11:58:01 | 2 | localhost | 5002 | secondary | prepare_promotion
11:58:01 | 1 | localhost | 5001 | draining | draining
11:58:01 | 2 | localhost | 5002 | prepare_promotion | prepare_promotion
11:58:02 | 2 | localhost | 5002 | prepare_promotion | stop_replication
11:58:02 | 1 | localhost | 5001 | draining | demote_timeout
11:58:03 | 1 | localhost | 5001 | demote_timeout | demote_timeout
11:58:04 | 2 | localhost | 5002 | stop_replication | stop_replication
11:58:05 | 2 | localhost | 5002 | stop_replication | wait_primary
11:58:05 | 1 | localhost | 5001 | demote_timeout | demoted
11:58:05 | 2 | localhost | 5002 | wait_primary | wait_primary
11:58:05 | 1 | localhost | 5001 | demoted | demoted
11:58:06 | 1 | localhost | 5001 | demoted | catchingup
11:58:06 | 1 | localhost | 5001 | catchingup | catchingup
11:58:08 | 1 | localhost | 5001 | catchingup | secondary
11:58:08 | 2 | localhost | 5002 | wait_primary | primary
11:58:08 | 1 | localhost | 5001 | secondary | secondary
11:58:08 | 2 | localhost | 5002 | primary | primary
Again, timings and PID numbers are not expected to be the same when you run the command on your own
setup.
Also note in the output that the command shows the whole set of transitions including when the old
primary is now a secondary node. The database is available for read-write traffic as soon as we reach the
state wait_primary.
Implementing a controlled switchover
It is generally useful to distinguish a controlled switchover to a failover. In a controlled switchover
situation it is possible to organise the sequence of events in a way to avoid data loss and lower
downtime to a minimum.
In the case of pg_auto_failover, because we use synchronous replication, we don't face data loss risks
when triggering a manual failover. Moreover, our monitor knows the current primary health at the time
when the failover is triggered, and drives the failover accordingly.
So to trigger a controlled switchover with pg_auto_failover you can use the same API as for a manual
failover:
$ pg_autoctl perform switchover
Because the subtelties of orchestrating either a controlled switchover or an unplanned failover are all
handled by the monitor, rather than the client side command line, at the client level the two command
pg_autoctl perform failover and pg_autoctl perform switchover are synonyms, or aliases.
Current state, last events
The following commands display information from the pg_auto_failover monitor tables pgautofailover.node
and pgautofailover.event:
$ pg_autoctl show state
$ pg_autoctl show events
When run on the monitor, the commands outputs all the known states and events for the whole set of
formations handled by the monitor. When run on a PostgreSQL node, the command connects to the monitor and
outputs the information relevant to the service group of the local node only.
For interactive debugging it is helpful to run the following command from the monitor node while e.g.
initializing a formation from scratch, or performing a manual failover:
$ watch pg_autoctl show state
Monitoring pg_auto_failover in Production
The monitor reports every state change decision to a LISTEN/NOTIFY channel named state. PostgreSQL logs
on the monitor are also stored in a table, pgautofailover.event, and broadcast by NOTIFY in the channel
log.
Replacing the monitor online
When the monitor node is not available anymore, it is possible to create a new monitor node and then
switch existing nodes to a new monitor by using the following commands.
1. Apply the STONITH approach on the old monitor to make sure this node is not going to show up again
during the procedure. This step is sometimes referred to as “fencing”.
2. On every node, ending with the (current) Postgres primary node for each group, disable the monitor
while pg_autoctl is still running:
$ pg_autoctl disable monitor --force
3. Create a new monitor node:
$ pg_autoctl create monitor ...
4. On the current primary node first, so that it's registered first and as a primary still, for each
group in your formation(s), enable the monitor online again:
$ pg_autoctl enable monitor postgresql://autoctl_node@.../pg_auto_failover
5. On every other (secondary) node, enable the monitor online again:
$ pg_autoctl enable monitor postgresql://autoctl_node@.../pg_auto_failover
See pg_autoctl disable monitor and pg_autoctl enable monitor for details about those commands.
This operation relies on the fact that a pg_autoctl can be operated without a monitor, and when
reconnecting to a new monitor, this process reset the parts of the node state that comes from the
monitor, such as the node identifier.
Trouble-Shooting Guide
pg_auto_failover commands can be run repeatedly. If initialization fails the first time -- for instance
because a firewall rule hasn't yet activated -- it's possible to try pg_autoctl create again.
pg_auto_failover will review its previous progress and repeat idempotent operations (create database,
create extension etc), gracefully handling errors.
FREQUENTLY ASKED QUESTIONS
Those questions have been asked in GitHub issues for the project by several people. If you have more
questions, feel free to open a new issue, and your question and its answer might make it to this FAQ.
I stopped the primary and no failover is happening for 20s to 30s, why?
In order to avoid spurious failovers when the network connectivity is not stable, pg_auto_failover
implements a timeout of 20s before acting on a node that is known unavailable. This needs to be added to
the delay between health checks and the retry policy.
See the Configuring pg_auto_failover part for more information about how to setup the different delays
and timeouts that are involved in the decision making.
See also pg_autoctl watch to have a dashboard that helps understanding the system and what's going on in
the moment.
The secondary is blocked in the CATCHING_UP state, what should I do?
In the pg_auto_failover design, the following two things are needed for the monitor to be able to
orchestrate nodes integration completely:
1. Health Checks must be successful
The monitor runs periodic health checks with all the nodes registered in the system. Those health
checks are Postgres connections from the monitor to the registered Postgres nodes, and use the
hostname and port as registered.
The pg_autoctl show state commands column Reachable contains "yes" when the monitor could connect
to a specific node, "no" when this connection failed, and "unknown" when no connection has been
attempted yet, since the last startup time of the monitor.
The Reachable column from pg_autoctl show state command output must show a "yes" entry before a new
standby node can be orchestrated up to the "secondary" goal state.
2. pg_autoctl service must be running
The pg_auto_failover monitor works by assigning goal states to individual Postgres nodes. The
monitor will not assign a new goal state until the current one has been reached.
To implement a transition from the current state to the goal state assigned by the monitor, the
pg_autoctl service must be running on every node.
When your new standby node stays in the "catchingup" state for a long time, please check that the node is
reachable from the monitor given its hostname and port known on the monitor, and check that the
pg_autoctl run command is running for this node.
When things are not obvious, the next step is to go read the logs. Both the output of the pg_autoctl
command and the Postgres logs are relevant. See the Should I read the logs? Where are the logs? question
for details.
Should I read the logs? Where are the logs?
Yes. If anything seems strange to you, please do read the logs.
As maintainers of the pg_autoctl tool, we can't foresee everything that may happen to your production
environment. Still, a lot of efforts is spent on having a meaningful output. So when you're in a
situation that's hard to understand, please make sure to read the pg_autoctl logs and the Postgres logs.
When using systemd integration, the pg_autoctl logs are then handled entirely by the journal facility of
systemd. Please then refer to journalctl for viewing the logs.
The Postgres logs are to be found in the $PGDATA/log directory with the default configuration deployed by
pg_autoctl create .... When a custom Postgres setup is used, please refer to your actual setup to find
Postgres logs.
The state of the system is blocked, what should I do?
This question is a general case situation that is similar in nature to the previous situation, reached
when adding a new standby to a group of Postgres nodes. Please check the same two elements: the monitor
health checks are successful, and the pg_autoctl run command is running.
When things are not obvious, the next step is to go read the logs. Both the output of the pg_autoctl
command and the Postgres logs are relevant. See the Should I read the logs? Where are the logs? question
for details.
Impossible / unresolveable state after crash - How to recover?
The pg_auto_failover Failover State Machine is great to simplify node management and orchestrate
multi-nodes operations such as a switchover or a failover. That said, it might happen that the FSM is
unable to proceed in some cases, usually after a hard crash of some components of the system, and mostly
due to bugs.
Even if we have an extensive test suite to prevent such bugs from happening, you might have to deal with
a situation that the monitor doesn't know how to solve.
The FSM has been designed with a last resort operation mode. It is always possible to unregister a node
from the monitor with the pg_autoctl drop node command. This helps the FSM getting back to a simpler
situation, the simplest possible one being when only one node is left registered in a given formation and
group (state is then SINGLE).
When the monitor is back on its feet again, then you may add your nodes again with the pg_autoctl create
postgres command. The command understands that a Postgres service is running and will recover from where
you left.
In some cases you might have to also delete the local pg_autoctl state file, error messages will instruct
you about the situation.
The monitor is a SPOF in pg_auto_failover design, how should we handle that?
When using pg_auto_failover, the monitor is needed to make decisions and orchestrate changes in all the
registered Postgres groups. Decisions are transmitted to the Postgres nodes by the monitor assigning
nodes a goal state which is different from their current state.
Consequences of the monitor being unavailable
Nodes contact the monitor each second and call the node_active stored procedure, which returns a goal
state that is possibly different from the current state.
The monitor only assigns Postgres nodes with a new goal state when a cluster wide operation is needed. In
practice, only the following operations require the monitor to assign a new goal state to a Postgres
node:
• a new node is registered
• a failover needs to happen, either triggered automatically or manually
• a node is being put to maintenance
• a node replication setting is being changed.
When the monitor node is not available, the pg_autoctl processes on the Postgres nodes will fail to
contact the monitor every second, and log about this failure. Adding to that, no orchestration is
possible.
The Postgres streaming replication does not need the monitor to be available in order to deliver its
service guarantees to your application, so your Postgres service is still available when the monitor is
not available.
To repair your installation after having lost a monitor, the following scenarios are to be considered.
The monitor node can be brought up again without data having been lost
This is typically the case in Cloud Native environments such as Kubernetes, where you could have a
service migrated to another pod and re-attached to its disk volume. This scenario is well supported by
pg_auto_failover, and no intervention is needed.
It is also possible to use synchronous archiving with the monitor so that it's possible to recover from
the current archives and continue operating without intervention on the Postgres nodes, except for
updating their monitor URI. This requires an archiving setup that uses synchronous replication so that
any transaction committed on the monitor is known to have been replicated in your WAL archive.
At the moment, you have to take care of that setup yourself. Here's a quick summary of what needs to be
done:
1. Schedule base backups
Use pg_basebackup every once in a while to have a full copy of the monitor Postgres database
available.
2. Archive WAL files in a synchronous fashion
Use pg_receivewal --sync ... as a service to keep a WAL archive in sync with the monitor Postgres
instance at all time.
3. Prepare a recovery tool on top of your archiving strategy
Write a utility that knows how to create a new monitor node from your most recent pg_basebackup
copy and the WAL files copy.
Bonus points if that tool/script is tested at least once a day, so that you avoid surprises on the
unfortunate day that you actually need to use it in production.
A future version of pg_auto_failover will include this facility, but the current versions don't.
The monitor node can only be built from scratch again
If you don't have synchronous archiving for the monitor set-up, then you might not be able to restore a
monitor database with the expected up-to-date node metadata. Specifically we need the nodes state to be
in sync with what each pg_autoctl process has received the last time they could contact the monitor,
before it has been unavailable.
It is possible to register nodes that are currently running to a new monitor without restarting Postgres
on the primary. For that, the procedure mentioned in Replacing the monitor online must be followed, using
the following commands:
$ pg_autoctl disable monitor
$ pg_autoctl enable monitor
AUTHOR
Microsoft
COPYRIGHT
Copyright (c) Microsoft Corporation. All rights reserved.
2.1 Nov 25, 2023 PG_AUTO_FAILOVER(1)