.TH ANVIL 8
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.SH NAME
anvil
\-
Postfix session count and request rate control
.SH "SYNOPSIS"
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\fBanvil\fR [generic Postfix daemon options]
.SH DESCRIPTION
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The Postfix \fBanvil\fR(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 \fBmaster\fR(8) server.
In the following text, \fBident\fR specifies a (service,
client) combination. The exact syntax of that information
is application-dependent; the \fBanvil\fR(8) server does
not care.
.SH "CONNECTION COUNT/RATE CONTROL"
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To register a new connection send the following request to
the \fBanvil\fR(8) server:
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\fBrequest=connect\fR
\fBident=\fIstring\fR
.fi
The \fBanvil\fR(8) server answers with the number of
simultaneous connections and the number of connections per
unit time for the (service, client) combination specified
with \fBident\fR:
.nf
\fBstatus=0\fR
\fBcount=\fInumber\fR
\fBrate=\fInumber\fR
.fi
To register a disconnect event send the following request
to the \fBanvil\fR(8) server:
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\fBrequest=disconnect\fR
\fBident=\fIstring\fR
.fi
The \fBanvil\fR(8) server replies with:
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\fBstatus=0\fR
.fi
.SH "MESSAGE RATE CONTROL"
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To register a message delivery request send the following
request to the \fBanvil\fR(8) server:
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\fBrequest=message\fR
\fBident=\fIstring\fR
.fi
The \fBanvil\fR(8) server answers with the number of message
delivery requests per unit time for the (service, client)
combination specified with \fBident\fR:
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\fBstatus=0\fR
\fBrate=\fInumber\fR
.fi
.SH "RECIPIENT RATE CONTROL"
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To register a recipient request send the following request
to the \fBanvil\fR(8) server:
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\fBrequest=recipient\fR
\fBident=\fIstring\fR
.fi
The \fBanvil\fR(8) server answers with the number of recipient
addresses per unit time for the (service, client) combination
specified with \fBident\fR:
.nf
\fBstatus=0\fR
\fBrate=\fInumber\fR
.fi
.SH "TLS SESSION NEGOTIATION RATE CONTROL"
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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 \fBanvil\fR(8) server:
.nf
\fBrequest=newtls\fR
\fBident=\fIstring\fR
.fi
The \fBanvil\fR(8) server answers with the number of new
TLS session requests per unit time for the (service, client)
combination specified with \fBident\fR:
.nf
\fBstatus=0\fR
\fBrate=\fInumber\fR
.fi
To retrieve new TLS session request rate information without
updating the counter information, send:
.nf
\fBrequest=newtls_report\fR
\fBident=\fIstring\fR
.fi
The \fBanvil\fR(8) server answers with the number of new
TLS session requests per unit time for the (service, client)
combination specified with \fBident\fR:
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\fBstatus=0\fR
\fBrate=\fInumber\fR
.fi
.SH "SECURITY"
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The \fBanvil\fR(8) server does not talk to the network or to local
users, and can run chrooted at fixed low privilege.
The \fBanvil\fR(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.
.SH DIAGNOSTICS
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Problems and transactions are logged to \fBsyslogd\fR(8).
Upon exit, and every \fBanvil_status_update_time\fR
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.
.SH BUGS
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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 \fBanvil\fR(8) server automatically discards client
request information after it expires. To prevent the
\fBanvil\fR(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.
.SH "CONFIGURATION PARAMETERS"
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On low-traffic mail systems, changes to \fBmain.cf\fR are
picked up automatically as \fBanvil\fR(8) processes run for
only a limited amount of time. On other mail systems, use
the command "\fBpostfix reload\fR" to speed up a change.
The text below provides only a parameter summary. See
\fBpostconf\fR(5) for more details including examples.
.IP "\fBanvil_rate_time_unit (60s)\fR"
The time unit over which client connection rates and other rates
are calculated.
.IP "\fBanvil_status_update_time (600s)\fR"
How frequently the \fBanvil\fR(8) connection and rate limiting server
logs peak usage information.
.IP "\fBconfig_directory (see 'postconf -d' output)\fR"
The default location of the Postfix main.cf and master.cf
configuration files.
.IP "\fBdaemon_timeout (18000s)\fR"
How much time a Postfix daemon process may take to handle a
request before it is terminated by a built-in watchdog timer.
.IP "\fBipc_timeout (3600s)\fR"
The time limit for sending or receiving information over an internal
communication channel.
.IP "\fBmax_idle (100s)\fR"
The maximum amount of time that an idle Postfix daemon process waits
for an incoming connection before terminating voluntarily.
.IP "\fBmax_use (100)\fR"
The maximal number of incoming connections that a Postfix daemon
process will service before terminating voluntarily.
.IP "\fBprocess_id (read-only)\fR"
The process ID of a Postfix command or daemon process.
.IP "\fBprocess_name (read-only)\fR"
The process name of a Postfix command or daemon process.
.IP "\fBsyslog_facility (mail)\fR"
The syslog facility of Postfix logging.
.IP "\fBsyslog_name (see 'postconf -d' output)\fR"
The mail system name that is prepended to the process name in syslog
records, so that "smtpd" becomes, for example, "postfix/smtpd".
.SH "SEE ALSO"
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smtpd(8), Postfix SMTP server
postconf(5), configuration parameters
master(5), generic daemon options
.SH "README FILES"
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Use "\fBpostconf readme_directory\fR" or
"\fBpostconf html_directory\fR" to locate this information.
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TUNING_README, performance tuning
.SH "LICENSE"
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The Secure Mailer license must be distributed with this software.
.SH "HISTORY"
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The anvil service is available in Postfix 2.2 and later.
.SH "AUTHOR(S)"
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Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA