WebSphere Extended Deployment introduces a new server type called an On Demand Router (ODR). The ODR is a special server that acts as a proxy, or intermediary for HTTP requests and the application servers committed to complete those requests. This is not a new concept, as most WebSphere users are used to proxy servers and their function. However, the ODR has some special abilities that are unique.

The ODR contains a component called an On Demand Configuration (ODC). The ODC automatically tries to get information about all the WebSphere Extended Deployment application servers and applications deployed in the cell. The ODC will dynamically configure the routing rules at runtime to allow the ODR to accurately route HTTP requests to those application servers.

Upon creation, an ODR will effectively be able to route HTTP requests to WebSphere Extended Deployment nodes.

The ODR has the additional ability to route work to non-WebSphere Extended Deployment nodes. This function allows an enterprise to take advantage of the unique routing abilities the ODR has on non-WebSphere nodes. The ODR routes work to non-XD servers in the same manner, but with some different configurations. The dynamic ability of the ODR does not fully extend outside of the XD environment, so the ODC is not functional. However, the advanced configuration options extend the ability of the ODR.

When routing work beyond WebSphere Extended Deployment nodes, you must configure your ODR with Generic Server Clusters, URI Groups, and Routing Rules.

• Generic server clusters is a user defined logical cluster of non-WebSphere Extended Deployment servers that the ODR can route to.
• URI groups are common application URIs that best define the content being served by the cluster.
• Routing rules use specific matching criteria that the ODR uses as comparison criteria when routing requests.

Generic server clusters define the boundaries, or endpoints of the cluster, but the ODR applies routing rules to the incoming requests, which in turn pull URI groups into the cluster. In effect the routing rules become the bond that relate generic server clusters to URI groups.

In a homogenous WebSphere Extended Deployment environment, the ODC function of the ODR is automated and dynamically creates and updates the routing table. In a mixed environment, generic server clusters, URI groups, and routing rules are used to create static routes without the dynamic application routing and server sensing capabilities of the ODC.