The Citrix NetScaler initially selects a server by using a load balancing method. With persistence configured, enabling the NetScaler to send any subsequent client requests to the selected server, the server can access state information for that client. If persistence is configured, it overrides the load balancing methods once the server has been selected. If the configured persistence applies to a service that is down, the NetScaler uses the load balancing methods to select a new service, and the new service becomes persistent for subsequent requests from the client. If the state of the selected service is “out of service”, it continues to serve the outstanding requests, but it does not allow new requests or connections. After the shutdown period elapses, no new requests or connections are directed to the service and the existing connections are closed.
The NetScaler creates a session-based persistence on the arriving SSL Session ID that is part of the SSL handshake process. The requests with the same SSL session ID are directed to the initially selected service. This persistence is used for SSL bridge type of services, and the NetScaler does not encrypt or decrypt data when it forwards the requests to the services. The NetScaler must maintain the data structures to keep track of the sessions. Keep in mind that persistence based on SSL session ID depends upon SSL sessions not renegotiating session IDs during a transaction.
To configure persistence based on SSL session IDs, in the Persistence list, select SSLSESSION.
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