High Availability with WebLogic Clusters - Oracle WebLogic Server 12c Advanced Administration - page 57

WebLogic can use either an external load balancer appliance/hardware such as the
BIG-IP F5 ( http://www.f5.com/products/big-ip ), a Web Server such as the
Apache HTTP Server configured with the WebLogic Web Server plug-in, or the embedded
WebLogic HttpClusterServlet configuration.
Load balancing options:
F External load balancer
F Web Server with plug-in
F WebLogic HttpClusterServlet configuration
For production environments, it is recommended to use a mixed architecture that includes
an external load balancer and a Web Server with the proxy plug-in. The HTTP requests will
be received and distributed by the external load balancer to the Web Servers, and the Web
Servers will then proxy the requests through the plug-in across the WebLogic Managed
Servers of the cluster. The WebLogic HttpClusterServlet configuration
is not recommended for use in production. The HTTP request sequence is as follows:
Client -> External Load Balancer -> Web Server + plug-in -> WebLogic cluster
Consider always including a Web Server tier + WebLogic plug-in to
distribute the HTTP requests across the WebLogic cluster.
Although it is possible to use only the external load balancers in the architecture, it's highly
recommended to include the Web Server and the plug-in. The plug-in contains all the logic
for the load balancing, session stickiness, and in particular the clustering failover with the
transparent connection failover.
More importantly, the plug-in is needed when setting up the workload
management through work managers, which will be seen later in this
topic.
Getting ready
The Web server plug-in can be used together with an Apache HTTP Server, Netscape IPlanet, or
Microsoft IIS web servers. This recipe will use the Apache installation from the previous recipe.
Unlike previous WebLogic versions, the plug-in is not included in the WebLogic
Server 12 c installation.