<?xml version="1.0"?>

<!--
  Copyright (C) Igor Sysoev
  Copyright (C) Nginx, Inc.
  -->

<!DOCTYPE module SYSTEM "../../../../dtd/module.dtd">

<module name="Module ngx_http_limit_req_module"
        link="/en/docs/http/ngx_http_limit_req_module.html"
        lang="en"
        rev="3">

<section id="summary">

<para>
The <literal>ngx_http_limit_req_module</literal> module (0.7.21) is used
to limit the request processing rate per a defined key,
in particular, the processing rate of requests coming
from a single IP address.
The limitation is done using the “leaky bucket” method.
</para>

</section>


<section id="example" name="Example Configuration">

<para>
<example>
http {
    limit_req_zone $binary_remote_addr zone=one:10m rate=1r/s;

    ...

    server {

        ...

        location /search/ {
            limit_req zone=one burst=5;
        }
</example>
</para>

</section>


<section id="directives" name="Directives">

<directive name="limit_req">
<syntax>
    <literal>zone</literal>=<value>name</value>
    [<literal>burst</literal>=<value>number</value>]
    [<literal>nodelay</literal>]</syntax>
<default/>
<context>http</context>
<context>server</context>
<context>location</context>

<para>
Sets the shared memory zone
and the maximum burst size of requests.
If the requests rate exceeds the rate configured for a zone,
their processing is delayed such that requests are processed
at a defined rate.
Excessive requests are delayed until their number exceeds the
maximum burst size
in which case the request is terminated with an error
<http-status code="503" text="Service Temporarily Unavailable"/>.
By default, the maximum burst size is equal to zero.
For example, the directives
<example>
limit_req_zone $binary_remote_addr zone=one:10m rate=1r/s;

server {
    location /search/ {
        limit_req zone=one burst=5;
    }
</example>
allow not more than 1 request per second at an average,
with bursts not exceeding 5 requests.
</para>

<para>
If delaying of excessive requests while requests are being limited is not
desired, the parameter <literal>nodelay</literal> should be used:
<example>
limit_req zone=one burst=5 nodelay;
</example>
</para>

</directive>


<directive name="limit_req_log_level">
<syntax>
<literal>info</literal> |
<literal>notice</literal> |
<literal>warn</literal> |
<literal>error</literal></syntax>
<default>error</default>
<context>http</context>
<context>server</context>
<context>location</context>
<appeared-in>0.8.18</appeared-in>

<para>
Sets the desired logging level
for cases when the server refuses to process requests
due to rate exceeding,
or delays request processing.
Logging level for delays is one point less than for refusals; for example,
if “<literal>limit_req_log_level notice</literal>” is specified,
delays are logged with the <literal>info</literal> level.
</para>

</directive>


<directive name="limit_req_status">
<syntax><value>code</value></syntax>
<default>503</default>
<context>http</context>
<context>server</context>
<context>location</context>
<appeared-in>1.3.15</appeared-in>

<para>
Sets the status code to return in response to rejected requests.
</para>

</directive>


<directive name="limit_req_zone">
<syntax>
    <value>$variable</value>
    <literal>zone</literal>=<value>name</value>:<value>size</value>
    <literal>rate</literal>=<value>rate</value></syntax>
<default/>
<context>http</context>

<para>
Sets parameters for a shared memory zone
that will keep states for various keys.
In particular, the state stores the current number of excessive requests.
The key is any non-empty value of the specified variable
(empty values are not accounted).
Usage example:
<example>
limit_req_zone $binary_remote_addr zone=one:10m rate=1r/s;
</example>
</para>

<para>
Here, the states are kept in a 10 megabyte zone “one”, and an
average request processing rate for this zone cannot exceed
1 request per second.
</para>

<para>
A client IP address serves as a key.
Note that instead of <var>$remote_addr</var>, the
<var>$binary_remote_addr</var> variable is used here,
that allows to decrease the state size down to 64 bytes.
One megabyte zone can keep about 16 thousand 64-byte states.
If the zone storage is exhausted, the server will return the
<http-status code="503" text="Service Temporarily Unavailable"/>
error to all further requests.
</para>

<para>
The rate is specified in requests per second (r/s).
If a rate of less than one request per second is desired,
it is specified in request per minute (r/m).
For example, half-request per second is 30r/m.
</para>

</directive>

</section>

</module>