Coyote Point Systems E350GX, Руководство по установке и администрированию

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Why Match Rules?
Equalizer Installation and Administration Guide 209
Figure 42 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 42) 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 42), 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 -- that is, the match rule
expression evaluates to
true -- no further match rules are checked against the request.
Equalizer makes a load balancing decision as follows:
1. If the request headers contain a cookie that specifies a server in the match rule’s server list, Equalizer sends the
request to the server in the cookie.
2. Otherwise, Equalizer sends the request to the server in the match rule’s server list that is selected by the load
balancing policy in effect for the match rule.