Backend Failover Overview of Origin Server Load Balancing and Failover

3-6 Oracle Fusion Middleware Administrators Guide for Oracle Web Cache Figure 3–3 Session Binding The steps for how session binding works for requests are as follows:

1. When a request first comes in, Oracle Web Cache uses load balancing to determine

to which origin server the request is forwarded. In this example, application server www.server2.com is selected.

2. If the requested object requires session binding, the origin server sends the session

information back to the client through Oracle Web Cache in the form of a cookie or an embedded URL parameter.

3. Oracle Web Cache sends subsequent requests for the session to the origin server

that established the session, bypassing load balancing. In this example, application server www.server2.com handles the subsequent requests. For instructions on configuring origin servers, see Section 2.12 . If you configure a cache cluster, when you configure session binding, do not select the Internal-Tracking mechanism option, as it does not work for cache clusters. The other mechanisms work for cache clusters. See Section 3.6.4 for further information. Notes: ■ When a session expires, Oracle Web Cache does not continue to bind the user session to the origin server. Instead, Oracle Web Cache uses load balancing to choose an origin server. To avoid pages being served past the client session expiration time, ensure that the session cookie expires before the origin server expires the client session. ■ If an origin server is busy, Oracle Web Cache disables session binding to that origin server. Application Servers server1-host server2-host server3-host Oracle Web Cache Web Browser 1 3 2 1 3 2 Incoming Requests to www.server.com:80 Configuring High Availability Solutions 3-7

3.3 Overview of Cache Clusters

In a cache cluster , multiple system components of Oracle Web Cache operate as one logical cache. This one logical cache is referred to as the cache cluster member . The cache cluster members communicate with one another to request cacheable content that is cached by another cache cluster member and to detect when a cache cluster member fails. Figure 3–4 shows an Oracle Web Cache cluster that contains three cache cluster members. As the figure shows, the cluster members communicate with one another as well as with the application Web servers and with the clients. Figure 3–4 Oracle Web Cache Cluster Architecture Oracle Web Cache uses the relative capacity of each cache instance to distribute the cached content among the cache cluster members. In effect, it assigns a cache cluster member to be the owner of a particular object. This content is called owned content . In addition to the owned content, Oracle Web Cache stores popular objects in the cache of each cluster member. These objects are known as on-demand content . By storing the on-demand content, Oracle Web Cache responds to requests for those objects quickly and decreases the number of cache misses. Fewer requests are sent to the application Web server. The result is improved performance. A cache cluster uses one configuration that is synchronized with all cluster members. The configuration contains general information, such as security, session information, Application Server Application Server Internet Oracle Web Cache Cluster