Load Balancer Configuration Requirements Load Balancers and the WebLogic Session Cookie

5-2 Using Clusters for Oracle WebLogic Server For instructions on setting up proxy plug-ins, see Section 10.2.9, Configure Proxy Plug-Ins.

5.1.1.1 How Session Connection and Failover Work with a Proxy Plug-in

For a description of connection and failover for HTTP sessions in a cluster with proxy plug-ins, see Section 6.2.2, Accessing Clustered Servlets and JSPs Using a Proxy.

5.1.2 Load Balancing HTTP Sessions with an External Load Balancer

Clusters that employ a hardware load balancing solution can use any load balancing algorithm supported by the hardware. These can include advanced load-based balancing strategies that monitor the utilization of individual machines.

5.1.2.1 Load Balancer Configuration Requirements

If you choose to use load balancing hardware instead of a proxy plug-in, it must support a compatible passive or active cookie persistence mechanism, and SSL persistence. ■ Passive Cookie Persistence Passive cookie persistence enables WebLogic Server to write a cookie containing session parameter information through the load balancer to the client. For information about the session cookie and how a load balancer uses session parameter data to maintain the relationship between the client and the primary WebLogic Server hosting a HTTP session state, see Section 5.1.2.2, Load Balancers and the WebLogic Session Cookie. . ■ Active Cookie Persistence You can use certain active cookie persistence mechanisms with WebLogic Server clusters, provided the load balancer does not modify the WebLogic Server cookie. WebLogic Server clusters do not support active cookie persistence mechanisms that overwrite or modify the WebLogic HTTP session cookie. If the load balancers active cookie persistence mechanism works by adding its own cookie to the client session, no additional configuration is required to use the load balancer with a WebLogic Server cluster. ■ SSL Persistence When SSL persistence is used, the load balancer performs all encryption and decryption of data between clients and the WebLogic Server cluster. The load balancer then uses the plain text cookie that WebLogic Server inserts on the client to maintain an association between the client and a particular server in the cluster.

5.1.2.2 Load Balancers and the WebLogic Session Cookie

A load balancer that uses passive cookie persistence can use a string in the WebLogic session cookie to associate a client with the server hosting its primary HTTP session state. The string uniquely identifies a server instance in the cluster. You must configure the load balancer with the offset and length of the string constant. The correct values for the offset and length depend on the format of the session cookie. The format of a session cookie is: sessionidprimary_server_idsecondary_server_id where: Load Balancing in a Cluster 5-3 ■ sessionid is a randomly generated identifier of the HTTP session. The length of the value is configured by the IDLength parameter in the session-descriptor element in the weblogic.xml file for an application. By default, the sessionid length is 52 bytes. ■ primary_server_id and secondary_server_id are 10 character identifiers of the primary and secondary hosts for the session. For general instructions on configuring load balancers, see Section 10.2.8, Configuring Load Balancers that Support Passive Cookie Persistence. Instructions for configuring BIG-IP, see Section B, Configuring BIG-IP Hardware with Clusters.

5.1.2.3 Related Programming Considerations