Oracle Web Cache Cluster-Wide Configuration Changes

9-22 Oracle Fusion Middleware High Availability Guide to the origin server that originally created the user session. Oracle Web Cache binds the user session to that particular origin server. Figure 9–7 shows how Oracle Web Cache supports objects that use session binding. Figure 9–7 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 Web 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 Web server www.server2.com handles the subsequent requests. 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 9.3.2.3, Oracle Web Cache Session Binding for instructions on configuring session binding.

9.3.2.4 Oracle Web Cache Cluster-Wide Configuration Changes

Oracle Web Cache provides cluster-wide capabilities through 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. 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 for Web Tier Components 9-23 Figure 9–8 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 9–8 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 synchronize to all cluster members. The configuration contains general information, such as security, session information, and caching rules, which is the same for all cluster members. It also contains cache-specific information, such as capacity, administration and other ports, resource limits, and log files, for each cluster member. Each member must be authenticated before it is added to the cache cluster. The authentication requires that the administration username and password of the Oracle Web Cache instance to be added be the same as the administration username and password of the cluster. Application Server Application Server Internet Oracle Web Cache Cluster 9-24 Oracle Fusion Middleware High Availability Guide When you add a cache to the cluster, the cache-specific information of the new cluster member is added to the configuration of the cache cluster. Then, Oracle Web Cache synchronizes the configuration to all members of the cluster. Because adding a new member changes the relative capacity of each Web cache, Oracle Web Cache uses the information about capacity to recalculate which cluster member owns which content. When cache cluster members detect the failure of another cluster member, the remaining cache cluster members automatically take over ownership of the content of the failing member. When the cache cluster member is reachable again, Oracle Web Cache again reassigns the ownership of the content. When you remove a Web cache from a cache cluster, the remaining cache cluster members take over ownership of the content of the removed member. In addition, the configuration information about the removed member is deleted from the configuration and the revised configuration is synchronized with the remaining cache cluster members. See Section 9.3.3.2, Configuring a Cache Cluster for instructions on configuring a cache cluster.

9.3.2.5 Oracle Web Cache as a Software Load Balancer