Coyote Point Systems Equalizer Especificações descarregar pdf (Página 319)

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, Equalizer can examine each request to determine if the content requested is

Text or Graphics, and send the request to the appropriate server pool. In this example, the servers need only hold

the content they are serving, text or graphics.

How Match Rules are Processed

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 a 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 pool for the match rule, Equalizer sends the

request to the server in the cookie.

Otherwise:

2. Equalizer sends the request to the server pool specified in the match rule that is selected by the load

balancing policy in effect for the match rule.

This process applies even if all the servers selected for the match rule are unavailable.

In this case, when the

match rule expression matches the request and all the servers in the match rule server list are unavailable, no reply

is sent to the client. Eventually, the client sees a connection timeout.

If the match expression evaluates to

false

, then each subsequent match rule in the list of match rules for the virtual

cluster is processed until a match occurs. All virtual clusters have a Default Match rule, which always evaluates to

true

and which will use the entire set of servers for load balancing. The Default Match rule is always processed

last.

Each virtual cluster can have any number of match rules, and each match rule can have arbitrarily complex match

expressions. Keep in mind that Equalizer interprets match rules for every Layer 7 cluster connection, so it is a

good idea to keep match rules as simple as possible.

Match Rule Order

When you add more than one match rule to a cluster, the order in which the match rules are processed is important

to system performance. Since processing a match rule requires system CPU and memory, the most efficient way

of ordering match rules is from the most common case to the least common case. In this way, you ensure that the

greatest number of client connections possible will process the first match rule and, if it matches the request, stop

processing match rules for that request.

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