Apache Module mod_proxy_balancer

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Description:	`mod_proxy` extension for load balancing
Status:	Extension
Module Identifier:	proxy_balancer_module
Source File:	mod_proxy_balancer.c
Compatibility:	Available in version 2.1 and later

Summary

This module requires the service of mod_proxy. It provides load balancing support for HTTP, FTP and AJP13 protocols

Load balancing scheduler algorithm is provided by not this module but other modules such as: mod_lbmethod_byrequests, mod_lbmethod_bytraffic and mod_lbmethod_bybusyness.

Thus, in order to get the ability of load balancing, mod_proxy, mod_proxy_balancer and at least one of load balancing scheduler algorithm modules have to be present in the server.

Warning

Do not enable proxying until you have secured your server. Open proxy servers are dangerous both to your network and to the Internet at large.

Directives

This module provides no directives.

Load balancer scheduler algorithm

At present, there are 3 load balancer scheduler algorithms available for use: Request Counting, Weighted Traffic Counting and Pending Request Counting. These are controlled via the lbmethod value of the Balancer definition. See the ProxyPass directive for more information.

Example of a balancer configuration

Before we dive into the technical details, here's an example of how you might use mod_proxy_balancer to provide load balancing between two back-end servers:

<Proxy balancer://mycluster> BalancerMember http://192.168.1.50:80 BalancerMember http://192.168.1.51:80 </Proxy> ProxyPass /test balancer://mycluster/

Exported Environment Variables

At present there are 6 environment variables exported:

BALANCER_SESSION_STICKY: This is assigned the stickysession value used in the current request. It is the cookie or parameter name used for sticky sessions
BALANCER_SESSION_ROUTE: This is assigned the route parsed from the current request.
BALANCER_NAME: This is assigned the name of the balancer used for the current request. The value is something like balancer://foo.
BALANCER_WORKER_NAME: This is assigned the name of the worker used for the current request. The value is something like http://hostA:1234.
BALANCER_WORKER_ROUTE: This is assigned the route of the worker that will be used for the current request.
BALANCER_ROUTE_CHANGED: This is set to 1 if the session route does not match the worker route (BALANCER_SESSION_ROUTE != BALANCER_WORKER_ROUTE) or the session does not yet have an established route. This can be used to determine when/if the client needs to be sent an updated route when sticky sessions are used.

Enabling Balancer Manager Support

This module requires the service of mod_status. Balancer manager enables dynamic update of balancer members. You can use balancer manager to change the balance factor or a particular member, or put it in the off line mode.

Thus, in order to get the ability of load balancer management, mod_status and mod_proxy_balancer have to be present in the server.

To enable load balancer management for browsers from the example.com domain add this code to your httpd.conf configuration file

<Location /balancer-manager> SetHandler balancer-manager Order Deny,Allow Deny from all Allow from .example.com </Location>

You can now access load balancer manager by using a Web browser to access the page http://your.server.name/balancer-manager