Server affinity

 

Server affinity is a technique that enables the Load Balancer to remember which server was chosen for a certain client at his initial request. Subsequent requests are then directed to the same server again.

If the affinity feature is disabled when a new TCP/IP connection is received from a client, Load Balancer picks the right server at that moment and forwards the packet to it. If a subsequent connection comes in from the same client, Load Balancer treats it as an unrelated connection, and again picks the most appropriate server at that moment.

Server affinity allows load balancing for those applications that need to preserve state across distinct connections from a client. Maintaining state is a requirement of many application encountered on the Internet today, including "shopping carts", home banking, and so on.

Some options available to maintain application state based on server affinity are:

"Stickyness" to source IP address

Passive cookie

Active cookie

URI

SSL session ID

The passive cookie, active cookie, and URI affinity options are rules based. They depend on the content of the client requests.

Important: Not all options are available for all components. For example, "Stickyness" to source IP address is the only affinity available for the Dispatcher component. We have noted at the end of each option for which components this affinity option applies.

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IBM is a trademark of the IBM Corporation in the United States, other countries, or both.