What is mod_icpquery?

Apache's mod_rewrite provides ways to map values to attributes using the directive RewriteMap. RewriteMap can use flat mappings files, hashed mapping files, internal functions and external rewriting programs. One not well known feature of mod_rewrite is to extend this functionality with internal functions, defined in a separate Apache module. This allows to do complex and time consuming mappings, since the mapping request does not have to be passed through a single communication pipe, as in the case of an external rewrite program.

Internet Cache Protocol

mod_icpquery is a package which can be used to find objects on caching servers by sending out a UDP query. This query conforms to RFC2186 also known as ICP and can be handled by various caching servers such as Squid. A cache server handling ICP should reply to an ICP-query with an ICP-response indicating if it holds the desired object in its cache or not. mod_icpquery is able to send UDP datagrams to a list of unicast and/or multicast IP-addresses.

Getting started

• Introduction and motivation for creating mod_icquery.
• Installation: How to build and install mod_icquery.
• Examples: Example setups for a typical usage of mod_icpquery.
• ConfigurationDirectives: The reference manual for mod_icpquery.
• MultipleInstantiation: In case you need the functionality for mod_icpquery more than once.
• Internals: For experts, knowing how to write Apache modules, which want to write their own mapping functionality, in order to extend mod_rewrite.

Enjoy, Jacob Rief