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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 ses- sions, or with too many successive requests within a configurable time in- terval. This server is designed to run under control by the Postfix mas- ter(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) combina- tion 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 fol- lowing 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 re- cent clients requests. No persistent state is kept because standard system library routines are not sufficiently robust for update-intensive applica- tions. 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) in- formation 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 re- ports multiple simultaneous clients, state is kept only for the last re- ported 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 al- ways 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 configura- tion 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. 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 Wietse Venema Google, Inc. 111 8th Avenue New York, NY 10011, USA ANVIL(8)
NAME | SYNOPSIS | DESCRIPTION | CONNECTION COUNT/RATE CONTROL | MESSAGE RATE CONTROL | RECIPIENT RATE CONTROL | TLS SESSION NEGOTIATION RATE CONTROL | AUTH RATE CONTROL | SECURITY | DIAGNOSTICS | BUGS | CONFIGURATION PARAMETERS | SEE ALSO | README FILES | LICENSE | HISTORY | AUTHOR(S)
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