Specifications

Chapter 8: Working with Match Rules
124 Equalizer Installation and Administration Guide
Figure56 Conceptual Example of Match Rule Processing
Most client requests are a mix of requests for text and graphics. Layer 7 processing without Match
Rules (top diagram in Figure 56) balances requests across all the available servers in the cluster, so
that each server will see a mix of text and graphics requests. This means that all text and graphics
must be available on each server.
Some sites may want to have one system serve only requests for graphics, and one system serve
only text requests. By adding appropriate Match Rules (bottom diagram in Figure 56), Equalizer can
examine each request to determine if the content requested is Text or Graphics, and send the request
to the appropriate server. In this example, the servers need only hold the content they are serving,
text or graphics.
Match Rule Processing
A match rule is like an if-then statement: an expression is evaluated and if it evaluates to true the
body of the match rule applies to the request.
A match expression is a combination of match functions with logical operators, and can be
arbitrarily complex. This allows for matching requests that have, for example:
(attribute A) AND NOT (attribute B)
If the match expression evaluates to true, then the data in the request has selected the match rule,
and the match body applies.. The match body contains statements that affect the subsequent
handling of the request.
Multiple match rules are checked in order. Once the data in the request selects a match rule, no
further match rules are checked against the request. Equalizer makes a load balancing decision
using the match body contents of the matching rule.