Combined Tier Architecture De-Militarized Zone DMZ Load Balancer Proxy Plug-In

9-2 Using Clusters for Oracle WebLogic Server ■ Object Tier The object tier provides Java objects for example, Enterprise JavaBeans or RMI classes and their associated business logic to a Web application. A WebLogic Server cluster that hosts EJBs provides an object tier.

9.1.3 Combined Tier Architecture

A cluster architecture in which all tiers of the Web application are deployed to a single WebLogic Server cluster is called a combined tier architecture.

9.1.4 De-Militarized Zone DMZ

The De-Militarized Zone DMZ is a logical collection of hardware and services that is made available to outside, untrusted sources. In most Web applications, a bank of Web servers resides in the DMZ to allow browser-based clients access to static HTML content. The DMZ may provide security against outside attacks to hardware and software. However, because the DMZ is available to untrusted sources, it is less secure than an internal system. For example, internal systems may be protected by a firewall that denies all outside access. The DMZ may be protected by a firewall that hides access to individual machines, applications, or port numbers, but it still permits access to those services from untrusted clients.

9.1.5 Load Balancer

In this document, the term load balancer describes any technology that distributes client connection requests to one or more distinct IP addresses. For example, a simple Web application may use the DNS round-robin algorithm as a load balancer. Larger applications generally use hardware-based load balancing solutions such as those from Alteon WebSystems, which may also provide firewall-like security capabilities. Load balancers provide the capability to associate a client connection with a particular server in the cluster, which is required when using in-memory replication for client session information. With certain load balancing products, you must configure the cookie persistence mechanism to avoid overwriting the WebLogic Server cookie which tracks primary and secondary servers used for in-memory replication. See Section 5.1.2, Load Balancing HTTP Sessions with an External Load Balancer, for more information.

9.1.6 Proxy Plug-In

A proxy plug-in is a WebLogic Server extension to an HTTP server—such as Apache, Netscape Enterprise Server, or Microsoft Internet Information Server—that accesses clustered servlets provided by a WebLogic Server cluster. The proxy plug-in contains the load balancing logic for accessing servlets and JSPs in a WebLogic Server cluster. Proxy plug-ins also contain the logic for accessing the replica of a clients session state if the primary WebLogic Server hosting the session state fails.

9.2 Recommended Basic Architecture