Ubuntu Manpage: gdnsdctl - Control socket client for gdnsd

NAME

       gdnsdctl - Control socket client for gdnsd

SYNOPSIS

         Usage: gdnsdctl [-c /etc/gdnsd] [-s <IP:port>] [-D] [-l] [-t 47] [-o] [-i] <action> [...]
           -c - Configuration directory (def /etc/gdnsd), for finding UNIX control socket path
           -s - TCP control socket address
           -D - Enable verbose debug output
           -l - Send logs to syslog rather than stderr
           -t - Timeout in seconds (def 47, range 5 - 300)
           -o - One-shot mode: do not retry soft failures (comms errors, replace-in-progress)
           -i - Ignore lack of a running daemon for stop, reload-zones, replace,
                and acme-dns-01-flush, reporting success instead of failure in those cases.
         Actions:
           stop - Stops the running daemon
           reload-zones - Reload the running daemon's zone data
           replace - Ask daemon to spawn a takeover replacement of itself (updates code, config, zone data)
           status - Checks the running daemon's status
           stats - Dumps JSON statistics from the running daemon
           states - Dumps JSON monitored states
           acme-dns-01 - Create ACME DNS-01 payloads from additional arguments:
                         <name> <payload> <name> <payload> ... [max %u payloads]
           acme-dns-01-flush - Flush (remove) all ACME DNS-01 payloads added above

DESCRIPTION

       gdnsdctl is the canonical control socket client for gdnsd.  All operations described above are
       synchronous and report success by exiting with exit status zero, or failure by non-zero.

       In general gdnsd and gdnsdctl support concurrent execution of disparate actions from multiple actors
       against a single daemon, and everything should eventually faithfully report success without any bugs
       caused by races, if there are no other issues.

       That is to say, for example, things should be reliable if your configuration management is routinely
       executing "gdnsdctl replace" for configuration updates, and another tool is independently routinely
       executing "gdnsdctl reload-zones" as it updates zonefile data, while a third set of tooling is doing
       "gdnsdctl acme-dns-01" commands, even if all 3 commands collide with near-perfect timing.  Eventually all
       3 "gdnsdctl" commands will exit, and the resulting state will have all of the configuration, zone data,
       and challenge updates.

       This is also true of multiple independent and overlapping executions of the same action, such as multiple
       "reload-zones" requests proceeding in parallel, or multiple "acme-dns-01" requests.

COMMANDLINE OPTION FLAGS

-c Set the configuration directory, defaults to /etc/gdnsd. This is used to find the main daemon's
configuration file and parse it, in case it sets a non-default "run_dir", which would change the
location of the daemon's UNIX control socket path.

-s This tells gdnsdctl to connect to the daemon over a TCP control socket instead of the usual local
UNIX domain socket. See the gdnsd.config(5) docs about "tcp_control" for more information about
configuring the server side of this.

-D Enables additional debug-level log output as appropriate.

-l Sends log output to syslog rather than the default stderr.

-t Sets the timeout in seconds (default 47) for the entire execution. This is enforced via a process-
level SIGALRM timer, but it can run slightly over time in corner cases.

-o One-shot mode. Normally, gdnsdctl will persistently retry to execute the action under soft failure
conditions. The soft failure conditions happen when the daemon is in the midst of a "replace"
operation, or when a communications error occurs after the connection is initially established (which
could be the racy result of catching bad timing with the old daemon shutting down during a "replace"
operation). This disables the retries and upgrades all soft (retryable) errors to hard (immediately-
fatal) errors.

-i Ignore-dead-daemon mode. Normally, all actions fail if no daemon is currently running. With this
flag set, if the daemon is not currently running, but the action is one of the limited set where the
intent would be accurately reflected by a future start of the daemon, gdnsdctl will return a
successful exit value in spite of the lack of a running daemon.

The set of commands which currently honor "-i" are: "reload-zones", "stop", "acme-dns-01-flush", and
"replace".

Actions

stop
Synchronously stops the running daemon. Exit status zero means the daemon was observed to stop as
commanded.

With "-i", exit status zero can also mean the daemon was already not running, which makes "gdnsdctl
-i stop" an idempotent stop.

reload-zones
Synchronously reloads the daemon's zonefiles. Exit status zero indicates the operation completed
successfully and the new data is visible to clients.

With "-i", exit status zero can also mean the daemon was not running (if it's started in the future,
the recently-updated zonefiles would be in effect).

replace
Asks the running daemon to spawn a replacement instance of itself. This can be used for daemon code
upgrades and/or configuration changes. The "replace" sequence is intended to have minimal
operational impact from most points of view: it's race-free, requests are not lost or dropped and
there is no pause in processing requests. Stats data is handed off seamlessly from the old instance
to the new one, as is any ephemeral ACME DNS-01 challenge data. The control socket remains available
for new connections at all times, but the actual processing of new connections is delayed for a short
span of time.

Commands from already-connected control socket clients (like gdnsdctl) can be denied with a soft
failure response during critical time windows of the replace sequence, but gdnsdctl will wait and
retry them afterwards.

The replacement daemon is initially executed as a child of the running daemon and thus inherits many
attributes of its execution environment. The old and new daemons coordinate a handoff process over
an inter-daemon control socket connection. The handoff process does its best to ensure that if the
new daemon fails at any stage of startup, the old daemon can continue operations as it was before.

DNS listening sockets are handed off in an overlapped fashion: there will be a brief window of time
where client requests can be routed to either daemon randomly, but there should never be a window
where service is unavailable. The control socket itself is handed off synchronously: the old daemon
stops accepting new connections before the new daemon begins accepting them, and the old daemon re-
starts accepting if the new daemon fails to succeed completely.

Once the old daemon claims the replacement process was successful, gdnsdctl will monitor the old
daemon's exit and then make a fresh connection to the control socket of the new daemon and check its
status. If all of this is successful, the replace command will finally exit with status zero. It
will exit with a non-zero status if any part of this operation fails for any reason, which should in
most conceivable cases leave the existing daemon fully functional.

All other daemon-state-changing gdnsdctl operations (anything but the readonly actions "status",
"stats", and "states") which might be initiated separately and concurrently are explicitly blocked by
the daemon while the critical part of the replace handoff sequence is in progress. gdnsdctl will, by
default, retry an action repeatedly until the replace finishes and lets the action through or it
reaches the "-t" timeout. The "-o" flag disables these retries, which will cause the state-changing
gdnsdctl actions to immediately fail during the critical replace window.

Normally, this command will fail if there is no running daemon. However, with "-i", exit status zero
can also mean the daemon was not running (if it's started in the future, the recently-updated
configuration or binary that triggered wanting to execute the "replace" request would then be in
effect).

The retry system works for "replace" vs "replace" as well: if you concurrently execute several
"gdnsdctl replace" commands, one will proceed first and the rest will wait in retry loops to each
take their turn replacing the daemon serially until they've all done so successfully, unless their
gdnsdctl "-t" timeout expires first (each new daemon will take some time to start, depending on the
zonefile count and configuration complexity).

status
Checks the running daemon's status, reporting its PID and version to stderr.

stats
Dumps JSON statistics from the running daemon to stdout.

states
Dumps JSON monitored states from any configured service health monitors.

acme-dns-01
Injects temporary ACME DNS-01 challenge response payloads as defined by
<https://tools.ietf.org/html/draft-ietf-acme-acme-14> into the running daemon. This is intended for
integration with scripts or services which generate signed certificates from an ACME-capable
certificate authority.

Two or more additional commandline arguments are required, in pairs of "name" and "payload", where
"name" is a valid domainname and "payload" is the challenge response payload (which, as a SHA-256
output encoded in base64url encoding, should be 43 bytes long and consist of only alphanumeric
characters plus "-" and "_"). A maximum of 100 separate payloads can be specified in a single
gdnsdctl invocation.

This example...

gdnsdctl acme-dns-01 example.org 0123456789012345678901234567890123456789012 www.example.org ABCDEFGHIJKLMNOPQRSTUVWXYZ-abcdefghijklmnop

... causes the daemon to temporarily respond to "TXT" requests for the name
"_acme-challenge.example.org." with the first payload above, and similarly with the second payload
for "_acme-challenge.www.example.org.".

Challenge payload responses injected by this command automatically expire after a short time. The
default is 10 minutes, and is configurable via the config option "acme_challenge_ttl". The actual
DNS TTL emitted with the "TXT" responses defaults to zero (which is highly recommended!) and is
controlled by the separate option "acme_challenge_dns_ttl".

Injecting responses for domainnames that are not within the scope of one of the statically-configured
zones will succeed, but the response to such queries will still be "REFUSED" (until such a zone later
appears, if ever).

If more than one payload is configured for a given name (in the same command, or in separate commands
less than the TTL window apart), multiple TXT records will be emitted. If there is any statically-
configured TXT data from zonefiles at a conflicting "_acme-challenge" name, the static TXT RRs will
also be served alongside any data from this mechanism.

As an implementail detail (quirk?) of this mechanism, any static zonefile RRs which have a first
label of "_acme-challenge" will automatically have their TTLs forced to the "acme_challenge_dns_ttl"
regardless of the TTL specified in the zonefile. This was the easiest way to ensure that we never
serve mixed TTL values in a single RR-set of TXT records, which is forbidden by RFC 2181.

The data injected by this mechanism persists through daemon "replace" operations, but not through a
full "stop" of the daemon. It also persists through zone data reloads, and in the case that data is
injected for a non-existent zone which then comes into existence through a reload, the challenge will
begin working after the reload.

acme-dns-01-flush
Immediately flushes all injected payload data from above ahead of its natural expiry. Mostly useful
for testing or for clearing up mistakes, but some integrations with spiky large volumes of challenges
may wish to flush data explicitly at points in time when there are no outstanding DNS-01 challenges.

This is another command that honors the "-i" flag: if "-i" is specified and the daemon is not
running, this command will report success, as a dead daemon has no challenge data to flush.

EXIT STATUS

       In general, all operations exit with status zero if and only if the operation is successful.  Errors  and
       most other output go to stderr, except in the case of JSON data dumps, which go to stdout.

COPYRIGHT AND LICENSE

       Copyright (c) 2012 Brandon L Black <blblack@gmail.com>

       This file is part of gdnsd.

       gdnsd  is  free  software:  you  can  redistribute it and/or modify it under the terms of the GNU General
       Public License as published by the Free Software Foundation, either version 3 of the License, or (at your
       option) any later version.

       gdnsd is distributed in the hope that it will be useful, but  WITHOUT  ANY  WARRANTY;  without  even  the
       implied  warranty  of  MERCHANTABILITY  or  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
       License for more details.

       You should have received a copy of the GNU  General  Public  License  along  with  gdnsd.   If  not,  see
       <http://www.gnu.org/licenses/>.

gdnsd 3.8.2                                        2024-03-31                                        GDNSDCTL(8)