Apache HTTP Server Version 2.1
Apache HTTP Server Version 2.1
| Description: | mod_proxy extension for
load balancing |
|---|---|
| Status: | Extension |
| Module Identifier: | proxy_balancer_module |
| Source File: | proxy_balancer.c |
| Compatibility: | Available in version 2.1 and later |
This module requires the service of mod_proxy. It provides load balancing support for
HTTP, FTP and AJP13 protocols
Thus, in order to get the ability of load balancing,
mod_proxy and mod_proxy_balancer
have to be present in the server.
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.
This module provides no directives.
The idea behind this scheduler is the following:
lbfactor is how much we expect this worker to work, or the workers's work quota.
lbstatus is how urgent this worker has to work to fulfill its quota of work.
The worker is a member of the load balancer, usually a remote host serving one of the supported protocols.
We distribute each worker's work quota to the worker, and then look which of them needs to work most urgently (biggest lbstatus). This worker is then selected for work, and its lbstatus reduced by the total work quota we distributed to all workers. Thus the sum of all lbstatus does not change.(*)
If some workers are disabled, the others will still be scheduled correctly.
If a balancer is configured as follows:
| worker | a | b | c | d |
|---|---|---|---|---|
| lbfactor | 25 | 25 | 25 | 25 |
| lbstatus | 0 | 0 | 0 | 0 |
And b gets disabled, the following schedule is produced:
| worker | a | b | c | d |
|---|---|---|---|---|
| lbstatus | -50 | 0 | 25 | 25 |
| lbstatus | -25 | 0 | -25 | 50 |
| lbstatus | 0 | 0 | 0 | 0 |
| (repeat) | ||||
That is it schedules: a c d a c d a c d ...
The following asymmetric configuration works as one would expect:
| worker | a | b |
|---|---|---|
| lbfactor | 70 | 30 |
| lbstatus | -30 | 30 |
| lbstatus | 40 | -40 |
| lbstatus | 10 | -10 |
| lbstatus | -20 | 20 |
| lbstatus | -50 | 50 |
| lbstatus | 20 | -20 |
| lbstatus | -10 | 10 |
| lbstatus | -40 | 40 |
| lbstatus | 30 | -30 |
| lbstatus | 0 | 0 |
| (repeat) | ||
That is after 10 schedules, the schedule repeats and 7 a are selected with 3 b interspersed.
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 foo.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 .foo.com
</Location>
You can now access load balancer manager by using a Web browser
to access the page
http://your.server.name/balancer-manager
