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ANVIL(8)                    System Manager's Manual                   ANVIL(8)




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

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).

       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)
              The mail system name that is prepended to the process name in
              syslog records, so that "smtpd" becomes, for example,
              "postfix/smtpd".

SEE ALSO
       smtpd(8), Postfix SMTP server
       postconf(5), configuration parameters
       master(5), generic daemon options

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



                                                                      ANVIL(8)