Session Persistence

Session persistence is the process by which all requests from the same client session are sent to the same back-end server. It can be used for any TCP or UDP protocol.

A pool serving static Web content usually has no requirement for session persistence; each page or image for a particular client can be served from a different machine with no ill effects. Another pool, serving an online shopping site, may use session persistence to ensure that a user's requests are always directed to the node holding details about their shopping basket.

The Virtual Traffic Manager offers several methods to identify requests which belong to the same session. A variety of different cookies can be used; persistence can be based on a rule; or the client’s IP address can be used to identify sessions. If incoming traffic is SSL-encrypted, the SSL session ID can be used.

You can choose what to do if a persistent session is lost. This might be due to invalid session data, or because the node handling it has failed. In this case you can choose to close the connection, have requests sent to a new node, or redirect the user to a specified URL such as an error page.

You can apply session persistence to a pool by clicking the Session Persistence link on the Pools > Edit page for that pool. Select a session persistence class and click the Update button.

Care must be taken when using a persistence class that is already in use by another pool. You should only re-use a persistence class if the nodes in this pool match those in the pool already using the class. Session affinity cannot be guaranteed where a persistence class is in use by two or more pools with different nodes.

Session Persistence is described in more detail in Session Persistence.