Cache Fill Plugin

The speed of the response served from the cache depends on the cache speed and the client filling the object. This dependency could significantly impact all the clients requesting the object. This plugin tries to eliminate the dependence by making the original request spawn a background request to fill the cache. The initial version of this plugin relays the initial request to the origin server instead of waiting for the background request to start filling the cache as there is no easier way to find the wait time. This plugin doesn’t provide any improvement for smaller objects but could also degrade the performance as two outgoing requests for every cache update.

Configuration

This plugin functions as either a global or per remap plugin, and it takes an optional argument for specifying a config file with inclusion or exclusion criteria. The config file can be specified both via an absolute path or via a relative path to the install dir

To activate the plugin in global mode, in plugin.config, simply add:

cache_fill.so --config <config-file>

To activate the plugin in per remap mode, in remap.config, simply append the below to the specific remap line:

@plugin=cache_fill.so @pparam=<config-file>

include/exclude

The plugin supports a config file that can specify exclusion or inclusion of background fetch based on any arbitrary header or client-ip

The contents of the config-file could be as below:

include User-Agent ABCDEF
exclude User-Agent *
exclude Content-Type text
exclude X-Foo-Bar text
exclude Content-Length <1000
exclude Client-IP 127.0.0.1
include Client-IP 10.0.0.0/16

The include configuration directive is only used when there is a corresponding exclude to exempt. For example, a single line directive, include Host example.com would not make the plugin only act on example.com. To achieve classic allow (only) lists, one would need to have a broad exclude line, such as:

exclude Host *
include Host example.com

range-request-only

When set to true, this plugin will only trigger a background fetch if a range header is present. Range headers include Range, If-Match, If-Modified-Since, If-None-Match, If-Range and If-Unmodified-Since. By default, this is set to false.

This would look like:

@plugin=cache_fill.so @pparam=--range-request-only

cache-range-req

When set to false. this plugin will not trigger a background fetch for range requests. By default, this is set to true. Note: you cannot set this to false and range-request-only to true.

This would look like:

@plugin=cache_fill.so @pparam=--cache-range-req=false

Functionality

Plugin decides to trigger a background fetch of the original (Client) request if the request/response is cacheable and cache status is TS_CACHE_LOOKUP_MISS/TS_CACHE_LOOKUP_HIT_STALE. This will work for range requests by making a background fetch and removing the range header. To disable this feature, set --cache-range-req=false

Future additions

• Fetching the original request from the cache.