Ubuntu Manpage: anvil - Postfix session count and request rate control

Provided by: postfix_3.10.2-1ubuntu1_amd64

NAME

       anvil - Postfix session count and request rate control

SYNOPSIS

       anvil [generic Postfix daemon options]

DESCRIPTION

       The  Postfix anvil(8) server maintains statistics about client connection counts or client request rates.
       This information can be used to defend against  clients  that  hammer  a  server  with  either  too  many
       simultaneous  sessions,  or  with too many successive requests within a configurable time interval.  This
       server is designed to run under control by the Postfix master(8) server.

       In the following text, ident specifies  a  (service,  client)  combination.  The  exact  syntax  of  that
       information is application-dependent; the anvil(8) server does not care.

CONNECTION COUNT/RATE CONTROL

       To register a new connection send the following request to the anvil(8) server:

           request=connect
           ident=string

       The anvil(8) server answers with the number of simultaneous connections and the number of connections per
       unit time for the (service, client) combination specified with ident:

           status=0
           count=number
           rate=number

       To register a disconnect event send the following request to the anvil(8) server:

           request=disconnect
           ident=string

       The anvil(8) server replies with:

           status=0

MESSAGE RATE CONTROL

       To register a message delivery request send the following request to the anvil(8) server:

           request=message
           ident=string

       The  anvil(8) server answers with the number of message delivery requests per unit time for the (service,
       client) combination specified with ident:

           status=0
           rate=number

RECIPIENT RATE CONTROL

       To register a recipient request send the following request to the anvil(8) server:

           request=recipient
           ident=string

       The anvil(8) server answers with the number of recipient  addresses  per  unit  time  for  the  (service,
       client) combination specified with ident:

           status=0
           rate=number

TLS SESSION NEGOTIATION RATE CONTROL

       The features described in this section are available with Postfix 2.3 and later.

       To  register a request for a new (i.e. not cached) TLS session send the following request to the anvil(8)
       server:

           request=newtls
           ident=string

       The anvil(8) server answers with the number of new TLS session requests per unit time for  the  (service,
       client) combination specified with ident:

           status=0
           rate=number

       To retrieve new TLS session request rate information without updating the counter information, send:

           request=newtls_report
           ident=string

       The  anvil(8)  server answers with the number of new TLS session requests per unit time for the (service,
       client) combination specified with ident:

           status=0
           rate=number

AUTH RATE CONTROL

       To register an AUTH request send the following request to the anvil(8) server:

           request=auth
           ident=string

       The anvil(8) server answers with the number of auth requests per unit  time  for  the  (service,  client)
       combination specified with ident:

           status=0
           rate=number

SECURITY

       The  anvil(8)  server  does  not talk to the network or to local users, and can run chrooted at fixed low
       privilege.

       The anvil(8) server maintains an in-memory table with information  about  recent  clients  requests.   No
       persistent  state  is  kept  because  standard  system  library  routines are not sufficiently robust for
       update-intensive applications.

       Although the in-memory state is kept only temporarily, this may require a lot of memory on  systems  that
       handle  connections  from  many  remote clients.  To reduce memory usage, reduce the time unit over which
       state is kept.

DIAGNOSTICS

       Problems and transactions are logged to syslogd(8) or postlogd(8).

       Upon exit, and every anvil_status_update_time seconds, the server logs the maximal count and rate  values
       measured,  together  with (service, client) information and the time of day associated with those events.
       In order to avoid unnecessary overhead, no measurements are done  for  activity  that  isn't  concurrency
       limited or rate limited.

BUGS

       Systems  behind network address translating routers or proxies appear to have the same client address and
       can run into connection count and/or rate limits falsely.

       In this preliminary implementation, a count (or rate) limited server process can  have  only  one  remote
       client  at  a time. If a server process reports multiple simultaneous clients, state is kept only for the
       last reported client.

       The anvil(8) server automatically discards client request information after it expires.  To  prevent  the
       anvil(8)  server  from  discarding  client request rate information too early or too late, a rate limited
       service should always register connect/disconnect events even when it does not explicitly limit them.

CONFIGURATION PARAMETERS

On low-traffic mail systems, changes to main.cf are picked up automatically as anvil(8) processes run for
only a limited amount of time. On other mail systems, use the command "postfix reload" to speed up a
change.

The text below provides only a parameter summary. See postconf(5) for more details including examples.

anvil_rate_time_unit (60s)
The time unit over which client connection rates and other rates are calculated.

anvil_status_update_time (600s)
How frequently the anvil(8) connection and rate limiting server logs peak usage information.

config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf configuration files.

daemon_timeout (18000s)
How much time a Postfix daemon process may take to handle a request before it is terminated by a
built-in watchdog timer.

ipc_timeout (3600s)
The time limit for sending or receiving information over an internal communication channel.

max_idle (100s)
The maximum amount of time that an idle Postfix daemon process waits for an incoming connection
before terminating voluntarily.

max_use (100)
The maximal number of incoming connections that a Postfix daemon process will service before
terminating voluntarily.

process_id (read-only)
The process ID of a Postfix command or daemon process.

process_name (read-only)
The process name of a Postfix command or daemon process.

syslog_facility (mail)
The syslog facility of Postfix logging.

syslog_name (see 'postconf -d' output)
A prefix that is prepended to the process name in syslog records, so that, for example, "smtpd"
becomes "prefix/smtpd".

Available in Postfix 3.3 and later:

service_name (read-only)
The master.cf service name of a Postfix daemon process.

README FILES

       Use "postconf readme_directory" or "postconf html_directory" to locate this information.
       TUNING_README, performance tuning

LICENSE

       The Secure Mailer license must be distributed with this software.

HISTORY

       The anvil service is available in Postfix 2.2 and later.

AUTHOR(S)

       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA

                                                                                                        ANVIL(8)