balancer balances requests across multiple origin servers.
To use this plugin, configure it in a
remap.config rule, specifying
a balancing policy and a set of origin servers. For example:
map http://foo.com http://foo.com \ @plugin=balancer.so @pparam=--policy=hash,url @pparam=one.bar.com @pparam=two.bar.com
replacement URL in the mapping rule is not used. The argument
--policy option is a comma-separated list of keywords.
The first keyword is the name of a balancing policy. The subsequent
keywords are used to refine the requested policy.
The remaining plugin arguments are balancer targets. Typically, these will be the host names of origin servers that requests should be balanced across. The target name may contain a colon-separated port number.
Hash Balancing Policy¶
hash balancing policy performs a consistent hash across the
set of origins. This minimizes the number of hash entries that must
be moved when the set of origin servers changes. An optional list
of hash fields follows the
hash keyword. Each specified hash
field is hashed to select an outbound origin server.
The following fields can be supplied to the hash:
- The request cache key. Note that the cache key will only be set if you have already chained a plugin that sets a custom cache key.
- The request URL. This is the default hash field that is used if no other fields are specified.
- The source IP address of the request.
- The destination IP address of the request.
Round Robin Balancing Policy¶
roundrobin balancing policy simply allocates requests to
origin servers in order. Over time, the number of requests received
by each origin should be approximately the same.
balancer plugin does not check the health of the origin
servers, however the plugin is fully reloadable so health checking
is usualy simple to implement. Most production environments already
have mechanisms to check service health. It is recommended that you
write a simple script to monitor this information and rewrite
remap.config when appropriate. Running
will reload the
balancer plugin with the new set of origin servers.