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d. Click on Commit to save your changes to the server configuration.

Maximum Connections Limits, Responders, and Hot Spares

When a maximum connections limit is set on all the servers in a cluster, it is often desirable to define either a

responder or a hot spare server for the cluster, so that any attempted connections to the cluster that occur after the

max connections limit has been reached are directed to the responder or hot spare instead of being refused or sent

to the server anyway because of a persistent connection.

In general, a Responder is easier to configure than setting up a separate server as a hot spare, since the responder

runs on Equalizer. However, while Responders are capable of returning only a single HTML page, a hot spare can

be configured to return multiple HTML pages and images. See "Cluster Types and How They're Used with

Equalizer" on page 260 for information on configuring a responder.

To use a hot spare, you would usually configure it on Equalizer as follows:

1. Set Max Connections to zero (0), so that all connection requests sent to the hot spare are accepted.

2. Enable the Hot Spare flag. This specifies that any requests refused by all the other server instances in a

server pool because they reached their Max Connections limit (or are down) will be forwarded to the hot

spare server.

3. Enable the Dont Persist flag so that connections made to the hot spare don’t persist. Each connection to the

cluster must first be load balanced amongst the other servers in the cluster and only go to the hot spare if all

the other servers have reached their Max Connections limit.

Interaction of Server Options and Connection

Processing

Server option settings have a direct influence on connection and request processing, particularly Layer 4 and Layer

7 persistence. (Note that persistence is set at the cluster level, but can be disabled for individual servers using the

Dont Persist option.) The hierarchy of server option settings is shown in the table below:

l Server disabled (initial weight = 0) - An initial weight of 0 tells Equalizer that no traffic should be sent to

the server, disabling the server. This option setting takes precedence over all other options (including

persistence, hot spare, etc.).

l Max Connections > 0 - If set to a non-zero value, Equalizer limits the total number of simultaneously open

connections to the server to that value. This limit is not overridden if the Hot Spare option is enabled on a

server, and is not overridden by a Layer 4 sticky record or Layer 7 persistence cookie for the server in an

incoming request.

l Quiesce Enabled - The server is

not

included in load balancing decisions, so that no

new

connections will

be made to this server. If a request in an incoming connection has an existing Layer 4 sticky record or Layer

7 cookie for a server, however, the request will be sent to that server even when Quiesce is enabled.

Note - If dont persist is also enabled on the server, the sticky record or cookie is ignored.

l Hot Spare Enabled - The server is

not

included in load balancing decisions, so that traffic is sent to this

server

only

when no other server in the cluster is available to accept client connections. If a request in an

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Equalizer Administration Guide

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