mod_limits.c
Marian Marinov <mm@yuhu.biz>
Ideas borrowed from David Jao <djao@dominia.org> (mod_limitipconn).


This apache module is aimed at protecting the web server during attacks.

It provides a few, very usefull, functionalities:

 * Limit the maximum number of simultaneous connections
 * Limit the maximum number of simultaneous connections per Vhost
 * Limit the maximum number of spawned processes with the same UID
 * Do not serve request if the load is over certain value

Example configuration:

---------------------------------------------------------------------------

ExtendedStatus On

LoadModule limits_module modules/mod_limits.so

<IfModule mod_limits.c>
	LimitMaxConnsPerVhost 20
	LimitMaxConnsPerUid 20
	LimitMaxConnsPerIP 30
	LimitMaxLoadAVG 10
	CheckLoadInterval 5
</IfModule>

---------------------------------------------------------------------------

Notes:

  This module will not function unless mod_status is loaded and the
  "ExtendedStatus On" directive is set.

  The limits defined by mod_limits.c apply to all IP addresses
  connecting to your Apache server. Currently there is no way to set
  different limits for different IP addresses.

  Connections in excess of the limit result in a stock 503 Service
  Temporarily Unavailable response. The job of returning a more useful
  error message to the client is left as an exercise for the reader.

  mod_limits sets the LIMITED environment variable to 1 whenever a
  request is denied. You can use this variable to distinguish accesses 
  that have been denied by this module. For example, a line like:

	CustomLog /var/log/httpd/access_log common env=!LIMITED

  in httpd.conf can be used to suppress logging of denied connections
  from /var/log/httpd/access_log.

  The options can be used within the main configuration or within 
  a VirtualHost configuration.

  You can have different limits for different vhosts.