Balancer Plugin¶
Note
All of the the features in this plugin (and more) are found in
parent.config
. As a result, this plugin is likely to be deprecated.
The 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
The replacement
URL in the mapping rule is not used. The argument
to the --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¶
The 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:
- key
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.
- url
The request URL. This is the default hash field that is used if no other fields are specified.
- srcaddr
The source IP address of the request.
- dstaddr
The destination IP address of the request.
Round Robin Balancing Policy¶
The 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.
Health Checking¶
The balancer
plugin does not check the health of the origin
servers, however the plugin is fully reloadable so health checking
is usually 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 traffic_ctl config reload
will reload the balancer
plugin with the new set of origin servers.