Oracle HTTP Server and Oracle WebLogic Server

9-4 Oracle Fusion Middleware High Availability Guide – The mod_wl_ohs module allows requests to be proxied from Oracle HTTP Server to Oracle WebLogic Server.

9.2.1.1 Oracle HTTP Server and Oracle WebLogic Server

Oracle HTTP Server does not require an Oracle WebLogic domain. However, Oracle HTTP Server is typically used in conjunction with an Oracle WebLogic Domain. The link to Oracle WebLogic managed servers is handled through the module mod_ wl_ohs. This module is configured by routing requests of a particular type, for example, JSPs, or by routing requests destined to a URL, to specific WebLogic Managed Servers. In a non high availability deployment, this destination is defined by specifying the host name and port on which the WebLogic manage server resides. In a high availability deployment, the WebLogic managed servers are typically clustered together. In such a deployment, a special mod_wl_ohs directive, WebLogicCluster, is used to specify a comma-separated list of cluster members. This list is not necessarily a complete list of cluster members. When a request requiring a WebLogic managed server is received, mod_wl_ohs send that request to one of the WebLogic cluster members listed in the directive. When the WebLogic managed server receives the request, it not only processes it, but it also sends a complete list of cluster members back to mod_wl_ohs. When mod_wl_ohs receives this updated list, it dynamically adds any previously unknown servers to the list of known servers, allowing all future requests to be load balanced across the full cluster member list. This process has the advantage of allowing new managed servers to be added to the cluster without updating mod_wl_ohs, or adding the Oracle HTTP Server. In an example scenario, assume that the WebLogic Cluster consists of WLS1, WLS2, and WLS3. Also assume that WLS1 and WLS2 are known to mod_wl_ohs. When mod_wl_ohs first receives a request, it attempts to send that request to either WLS1 or WLS2, if it is successful then the list is updated to include WLS3 for future requests. If, however, WLS1 and WLS2 are unavailable, but WLS3 is available, the request is rejected because mod_wl_ohs has no way of knowing WLS3 exists. When using the Oracle HTTP server with an Oracle WebLogic domain, Oracle recommends associating Oracle HTTP Server with the WebLogic domain. This allows the Oracle HTTP Server to be incorporated into the Oracle Fusion Middleware Console for centralized management and monitoring. For more information Oracle WebLogic clusters, see Oracle Fusion Middleware Using Clusters for Oracle WebLogic Server.

9.2.1.2 Oracle HTTP Server External Dependencies