> Apache2.2 中文手册 > mod_proxy_balancer

Apache模块 mod_proxy_balancer

说明 mod_proxy的扩展,提供负载平衡支持
状态 扩展(E)
模块名 proxy_balancer_module
源文件 proxy_balancer.c
兼容性 仅在 Apache 2.1 及以后的版本中可用


This module requires the service of mod_proxy. It provides load balancing support for HTTP, FTPAJP13 protocols

Thus, in order to get the ability of load balancing, mod_proxymod_proxy_balancer have to be present in the server.




Proxy directive for more information.


Request Counting Algorithm

Enabled via lbmethod=byrequests, the idea behind this scheduler is that we distribute the requests among the various workers to ensure that each gets their configured share of the number of requests. It works as follows:

lbfactor is how much we expect this worker to work, or the workers's work quota. This is a normalized value representing their "share" of the amount of work to be done.

lbstatus is how urgent this worker has to work to fulfill its quota of work.

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(*) and we distribute the requests as desired.

If some workers are disabled, the others will still be scheduled correctly.

for each worker in workers
    worker lbstatus += worker lbfactor
    total factor    += worker lbfactor
    if worker lbstatus > candidate lbstatus
        candidate = worker

candidate lbstatus -= total factor

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

That is it schedules: a c d a c d a c d ... Please note that:

worker a b c d
lbfactor 25 25 25 25

Has the exact same behavior as:

worker a b c d
lbfactor 1 1 1 1

This is because all values of lbfactor are normalized with respect to the others. For:

worker a b c
lbfactor 1 4 1

worker b will, on average, get 4 times the requests that ac will.

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

That is after 10 schedules, the schedule repeats and 7 a are selected with 3 b interspersed.


Weighted Traffic Counting Algorithm

Enabled via lbmethod=bytraffic, the idea behind this scheduler is very similar to the Request Counting method, with the following changes:

lbfactor is how much traffic, in bytes, we want this worker to handle. This is also a normalized value representing their "share" of the amount of work to be done, but instead of simply counting the number of requests, we take into account the amount of traffic this worker has seen.

If a balancer is configured as follows:

worker a b c
lbfactor 1 2 1

Then we mean that we want b to process twice the amount of bytes than ac should. It does not necessarily mean that b would handle twice as many requests, but it would process twice the I/O. Thus, the size of the request and response are applied to the weighting and selection algorithm.


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_statusmod_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

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