Synopsis

This module makes it possible to limit the number of simultaneous connections for the assigned session or as a special case, from one address.

Example configuration

http {
  limit_zone   one  $binary_remote_addr  10m;
 
  server {
    location /download/ {
      limit_conn   one  1;
    }
  }
}

Directives

limit_zone

This directive is made obsolete in version 1.1.8, an equivalent limit_conn_zone directive with a changed syntax should be used instead:

limit_conn_zone $variable zone=name:size;

Directive describes the zone, in which the session states are stored.
The numbers of sessions is determined by the assigned variable, it depends on the size of the used Variable and memory_max_size value.

Example of the use:

limit_zone one $binary_remote_addr 10m;

The address of client is used as the session. Notice that the variable $binary_remote_addr is used instead of $remote_addr.

The length of the values of the variable of $remote_addr can be from 7 to 15 bytes; therefore size state is equal to 32 or 64 bytes.

Length of all values of the variable of $binary_remote_addr is always 4 bytes and the size of the state is always 32 bytes.

When the zone size is 1M then it is possible to handle 32000 sessions with 32 bytes/session.

limit_conn

Directive assigns the maximum number of simultaneous connections for one session. With exceeding of this number the request completes by the code "Service unavailable" (503).

For example, the directive:

limit_zone   one  $binary_remote_addr  10m;
 
server {
  location /download/ {
  limit_conn   one  1;
}

This allows not more than one simultaneous connection from one address.

limit_conn_log_level

Sets the error log level used when a connection limit is reached

References

Original Documentation