1ANVIL(8) System Manager's Manual ANVIL(8)
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6 anvil - Postfix session count and request rate control
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9 anvil [generic Postfix daemon options]
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12 The Postfix anvil(8) server maintains statistics about client connec‐
13 tion counts or client request rates. This information can be used to
14 defend against clients that hammer a server with either too many simul‐
15 taneous sessions, or with too many successive requests within a config‐
16 urable time interval. This server is designed to run under control by
17 the Postfix master(8) server.
18 In the following text, ident specifies a (service, client) combination.
20 The exact syntax of that information is application-dependent; the
21 anvil(8) server does not care.
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24 To register a new connection send the following request to the anvil(8)
25 server:
26 request=connect
28 ident=string
29 The anvil(8) server answers with the number of simultaneous connections
31 and the number of connections per unit time for the (service, client)
32 combination specified with ident:
33 status=0
35 count=number
36 rate=number
37 To register a disconnect event send the following request to the
39 anvil(8) server:
40 request=disconnect
42 ident=string
43 The anvil(8) server replies with:
45 status=0
47
49 To register a message delivery request send the following request to
50 the anvil(8) server:
51 request=message
53 ident=string
54 The anvil(8) server answers with the number of message delivery
56 requests per unit time for the (service, client) combination specified
57 with ident:
58 status=0
60 rate=number
61
63 To register a recipient request send the following request to the
64 anvil(8) server:
65 request=recipient
67 ident=string
68 The anvil(8) server answers with the number of recipient addresses per
70 unit time for the (service, client) combination specified with ident:
71 status=0
73 rate=number
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76 The features described in this section are available with Postfix 2.3
77 and later.
78 To register a request for a new (i.e. not cached) TLS session send the
80 following request to the anvil(8) server:
81 request=newtls
83 ident=string
84 The anvil(8) server answers with the number of new TLS session requests
86 per unit time for the (service, client) combination specified with
87 ident:
88 status=0
90 rate=number
91 To retrieve new TLS session request rate information without updating
93 the counter information, send:
94 request=newtls_report
96 ident=string
97 The anvil(8) server answers with the number of new TLS session requests
99 per unit time for the (service, client) combination specified with
100 ident:
101 status=0
103 rate=number
104
106 The anvil(8) server does not talk to the network or to local users, and
107 can run chrooted at fixed low privilege.
108 The anvil(8) server maintains an in-memory table with information about
110 recent clients requests. No persistent state is kept because standard
111 system library routines are not sufficiently robust for update-inten‐
112 sive applications.
113 Although the in-memory state is kept only temporarily, this may require
115 a lot of memory on systems that handle connections from many remote
116 clients. To reduce memory usage, reduce the time unit over which state
117 is kept.
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120 Problems and transactions are logged to syslogd(8).
121 Upon exit, and every anvil_status_update_time seconds, the server logs
123 the maximal count and rate values measured, together with (service,
124 client) information and the time of day associated with those events.
125 In order to avoid unnecessary overhead, no measurements are done for
126 activity that isn't concurrency limited or rate limited.
127
129 Systems behind network address translating routers or proxies appear to
130 have the same client address and can run into connection count and/or
131 rate limits falsely.
132 In this preliminary implementation, a count (or rate) limited server
134 process can have only one remote client at a time. If a server process
135 reports multiple simultaneous clients, state is kept only for the last
136 reported client.
137 The anvil(8) server automatically discards client request information
139 after it expires. To prevent the anvil(8) server from discarding
140 client request rate information too early or too late, a rate limited
141 service should always register connect/disconnect events even when it
142 does not explicitly limit them.
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145 On low-traffic mail systems, changes to main.cf are picked up automati‐
146 cally as anvil(8) processes run for only a limited amount of time. On
147 other mail systems, use the command "postfix reload" to speed up a
148 change.
149 The text below provides only a parameter summary. See postconf(5) for
151 more details including examples.
152 anvil_rate_time_unit (60s)
154 The time unit over which client connection rates and other rates
155 are calculated.
156 anvil_status_update_time (600s)
158 How frequently the anvil(8) connection and rate limiting server
159 logs peak usage information.
160 config_directory (see 'postconf -d' output)
162 The default location of the Postfix main.cf and master.cf con‐
163 figuration files.
164 daemon_timeout (18000s)
166 How much time a Postfix daemon process may take to handle a
167 request before it is terminated by a built-in watchdog timer.
168 ipc_timeout (3600s)
170 The time limit for sending or receiving information over an
171 internal communication channel.
172 max_idle (100s)
174 The maximum amount of time that an idle Postfix daemon process
175 waits for an incoming connection before terminating voluntarily.
176 max_use (100)
178 The maximal number of incoming connections that a Postfix daemon
179 process will service before terminating voluntarily.
180 process_id (read-only)
182 The process ID of a Postfix command or daemon process.
183 process_name (read-only)
185 The process name of a Postfix command or daemon process.
186 syslog_facility (mail)
188 The syslog facility of Postfix logging.
189 syslog_name (see 'postconf -d' output)
191 The mail system name that is prepended to the process name in
192 syslog records, so that "smtpd" becomes, for example, "post‐
193 fix/smtpd".
194
196 smtpd(8), Postfix SMTP server
197 postconf(5), configuration parameters
198 master(5), generic daemon options
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201 Use "postconf readme_directory" or "postconf html_directory" to locate
202 this information.
203 TUNING_README, performance tuning
204
206 The Secure Mailer license must be distributed with this software.
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209 The anvil service is available in Postfix 2.2 and later.
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212 Wietse Venema
213 IBM T.J. Watson Research
214 P.O. Box 704
215 Yorktown Heights, NY 10598, USA
216 ANVIL(8)