In the navigator frame, select Operations Cache Operations. See Select the cache, and then click Start, Stop, or Restart.

3 Configuring High Availability Solutions 3-1 3 Configuring High Availability Solutions This chapter describes how to configure and implement high availability solutions using Oracle Web Cache. This chapter includes the following topics: ■ Section 3.1, Overview of Origin Server Load Balancing and Failover ■ Section 3.2, Overview of Session Binding ■ Section 3.3, Overview of Cache Clusters ■ Section 3.4, Overview of High Availability without a Hardware Load Balancer ■ Section 3.5, Configuring Session Binding ■ Section 3.6, Configuring a Cache Cluster for Caches Using the Same Oracle WebLogic Server ■ Section 3.7, Configuring a Cache Cluster for Unassociated Caches or Caches Using Different Oracle WebLogic Servers ■ Section 3.8, Configuring Oracle Web Cache as a Software Load Balancer ■ Section 3.9, Configuring Microsoft Windows Network Load Balancing

3.1 Overview of Origin Server Load Balancing and Failover

You can configure Oracle Web Cache with the application Web servers or proxy servers to which it sends cache misses. Typically, Oracle Web Cache uses application Web servers for internal sites and proxy servers for external sites outside a firewall. This section covers the following concepts: ■ Section 3.1.1, Surge Protection ■ Section 3.1.2, Stateless Load Balancing ■ Section 3.1.3, Backend Failover For instructions on configuring origin servers, see Section 2.11.2 .

3.1.1 Surge Protection

Oracle Web Cache passes requests for non-cacheable, stale, or missing objects to origin servers. To prevent an overload of requests on the origin servers, Oracle Web Cache has a surge protection feature that enables you to set a limit on the number of concurrent requests that the origin servers can handle. When the limit is reached, subsequent requests are queued. If the queue is full, then Oracle Web Cache rejects the request and serves a site busy error page to the client that initiated the request. 3-2 Oracle Fusion Middleware Administrators Guide for Oracle Web Cache

3.1.2 Stateless Load Balancing

Most Web sites are served by multiple origin servers running on multiple computers that share the load of HTTP and HTTPS requests. All requests that Oracle Web Cache cannot serve are passed to the origin servers. Oracle Web Cache balances the load among origin servers by determining the percentage of the available capacity , the weighted available capacity of each origin server. Oracle Web Cache sends a request to the origin server with the most weighted available capacity. The weighted available capacity is determined by the following formula: Capacity - Load Capacity where: ■ Capacity is the maximum number of concurrent connections that the origin server can accept ■ Load is the number of connections currently in use If the weighted available capacity is equal for multiple origin servers, Oracle Web Cache sends requests to the origin servers using round robin . With round robin, the first origin server in the list of configured servers receives the request, then the second origin server receives the second request. If the weighted available capacity is not equal, Oracle Web Cache sends the request to the origin server with the most available capacity. If the load of origin servers is equivalent, Oracle Web Cache continues to use round robin, even when capacity is not equal for origin servers. Therefore, it is possible to see an even distribution of requests to origin server when the capacities are not configured to be the same. To configure load balancing for a site, set the capacity of each origin server, and create one site-to-server mapping that maps all the applicable origin servers to the site. For further information about configuration, see: ■ Section 2.11.2 for instructions on specifying capacity ■ Section 2.11.4 for instructions on creating site-to-server mappings Figure 3–1 shows two sites, www.company.com:80 and www.server.com:80. The site www.company.com:80 is supported by application servers company-host1 and company-host2 with capacities of 50 each. The site www.server.com:80 is supported by application servers server-host1, server-host2, and server-host3 with capacities of 150, 50, and 50, respectively. Configuring High Availability Solutions 3-3 Figure 3–1 Load Balancing Assuming all application Web servers have an initial load of 0, Oracle Web Cache distributes the requests to www.company.com:80 and www.server.com:80 in the following manner: ■ Oracle Web Cache distributes the requests to www.company.com:80 between the two application servers using round robin. Oracle Web Cache distributes the requests to company-host1 and company-host2 between the two application servers so that they maintain an equal load. The first request is sent to company-host1. The second request is sent to company-host2 if company-host1 is still processing the first request. The third and subsequent requests are sent to the application server that has the highest weighted available capacity. When the capacities are equal, Oracle Web Cache uses round robin to distribute requests. Application Servers company1-host company2-host Oracle Web Cache Web Browser Web Browser Web Browser Web Browser Incoming Requests to www.company.com:80 Incoming Requests to www.server.com:80 Capacity:50 Capacity:50 Application Servers server1-host server2-host server3-host Capacity:150 Capacity:50 Capacity:50 Load balancing of requests Load balancing of requests Site: www.server.com:80 Site: www.company.com:80