Connection with Load Balancing Hardware Failover with Load Balancing Hardware

Failover and Replication in a Cluster 6-9

6.2.3.1 Connection with Load Balancing Hardware

Figure 6–3 illustrates the connection procedure for a client accessing a cluster through a load balancer. Figure 6–3 Connection with Load Balancing Hardware When the client of a Web application requests a servlet using a public IP address: 1. The load balancer routes the clients connection request to a WebLogic Server cluster in accordance with its configured policies. It directs the request to WebLogic Server A. 2. WebLogic Server A acts as the primary host of the clients servlet session state. It uses the ranking system described in Section 6.2.1.2, Using Replication Groups to select a server to host the replica of the session state. In the example above, WebLogic Server B is selected to host the replica. 3. The client is instructed to record the location of WebLogic Server instances A and B in a local cookie. If the client does not allow cookies, the record of the primary and secondary servers can be recorded in the URL returned to the client via URL rewriting. 6-10 Using Clusters for Oracle WebLogic Server 4. As the client makes additional requests to the cluster, the load balancer uses an identifier in the client-side cookie to ensure that those requests continue to go to WebLogic Server A rather than being load-balanced to another server in the cluster. This ensures that the client remains associated with the server hosting the primary session object for the life of the session.

6.2.3.2 Failover with Load Balancing Hardware

Should Server A fail during the course of the clients session, the clients next connection request to Server A also fails, as illustrated in Figure 6–4 . Figure 6–4 Failover with Load Balancing Hardware In response to the connection failure: 1. The load balancing hardware uses its configured policies to direct the request to an available WebLogic Server in the cluster. In the above example, assume that the load balancer routes the clients request to WebLogic Server C after WebLogic Server A fails. Note: You must enable WebLogic Server URL rewriting capabilities to support clients that disallow cookies, as described in Section 6.2.2.1.1, Using URL Rewriting to Track Session Replicas. Failover and Replication in a Cluster 6-11 2. When the client connects to WebLogic Server C, the server uses the information in the clients cookie or the information in the HTTP request if URL rewriting is used to acquire the session state replica on WebLogic Server B. The failover process remains completely transparent to the client. WebLogic Server C becomes the new host for the clients primary session state, and WebLogic Server B continues to host the session state replica. This new information about the primary and secondary host is again updated in the clients cookie, or via URL rewriting.

6.2.4 Session State Replication Across Clusters in a MANWAN