Apache 2.2.x

Apache HTTP Server versions 2.2.x provides load balancing tools through two Apache modules

The two modules are:

The mod_proxy_balancer module provides support for HTTP requests load balancing. The mod_headers module provides HTTP cookies management needed by the Cookie-based request processing. For Sessionless request processing, the mod_headers module is not required.

Sessionless requests

The following example shows how to configure Apache 2.2.x to do load balancing for sessionless requests. It assumes the architecture illustrated by Session-bound request processing.

<IfModule mod_proxy.c>
  ProxyPass / balancer://GASFarm
  <Proxy balancer://GASFarm>
    BalancerMember http://GAS1.corporate.com
    BalancerMember http://GAS2.corporate.com
  </Proxy>
</IfModule>

These configuration entries can be put at the server level in the httpd.conf file.
The ProxyPass instruction tells the module to rewrite all incoming requests so that they are routed to the GASFarm web farm.
The <Proxy balancer://GASFarm>...</Proxy> block defines which are the members of GASFarm web farm.
The BalancerMember instructions declare two HTTP web server members of GASFarm web farm: GAS1.corporate.com and GAS2.corporate.com.

For example, the http://localhost/ws/r/echo URL will be rewritten to http://GAS1.corporate.com/ws/r/echo, assuming that the GAS1.corporate.com server has been chosen.

Session-bound requests

The following example shows how to configure Apache 2.2.x to do load balancing for session-bound requests. It assumes the architecture illustrated by Session-bound request processing. The example illustrates cookie-based request routing.

<IfModule mod_proxy.c>
  ProxyPass / balancer://GASFarm stickysession=GAS_AFFINITY
  <Proxy balancer://GASFarm>
    BalancerMember http://GAS1.corporate.com route=GAS1
    BalancerMember http://GAS2.corporate.com route=GAS2
  </Proxy>
</IfModule>

<IfModule mod_headers.c>
  Header add Set-Cookie "GAS_AFFINITY=balancer.%{BALANCER_WORKER_ROUTE}e;
  path=/; domain=.corporate.com" env=BALANCER_WORKER_ROUTE
</IfModule>

These configuration entries can be put at the server level in the httpd.conf file.
The ProxyPass instruction tells the module to rewrite all incoming requests so that they are routed to the GASFarm web farm. The stickysession parameter gives the name of the cookie to use to retrieve the GAS that holds the session.
The <Proxy balancer://GASFarm>...</Proxy> block declares which are the members of GASFarm web farm.
The BalancerMember instructions declare two HTTP web server members of the GASFarm web farm: GAS1.corporate.com and GAS2.corporate.com. The route parameter gives the name of the route associated with that member. If that route name is found in the request cookie, then that member will be chosen.
The Header instruction will set, in the HTTP response, the cookie named GAS_AFFINITY to value balancer.BALANCER_WORKER_ROUTE. The BALANCER_WORKER_ROUTE variable is assigned to the route of the GASFarm member that has be chosen for the current request. Lastly, the env parameter tells the module to set that cookie only if the BALANCER_WORKER_ROUTE variable is defined.

For example, the http://localhost/ua/r/gwc-demo URL will be rewritten to http://GAS1.corporate.com/ua/r/gwc-demo, assuming that the GAS1.corporate.com server has been chosen.