On-demand router
The topology of a WebSphere XD environment is different than a typical cluster setup. Most notable is the introduction of an On Demand Router (ODR) node. Figure | -1 shows an example of WebSphere Commerce running in an XD environment.
Figure B-1 WebSphere Commerce in a WebSphere XD environment
The ODR routes traffic, controls logic, and handles caching and partition decision-making in the WebSphere XD environment. It is an application that runs on WebSphere Application Server.
All requests are routed through the ODR. It is possible to have a cluster of ODRs so that the routing does not become a bottleneck in the system. In a partitioned environment, the ODR extracts the partition name from the HTTP request and routes it to the application server hosting the application instance that is currently serving this partition.
The partition name is constructed from information contained in the HTTP request. HTTP Partitioning assumes incoming HTTP requests contain sufficient information to identify the partition associated with the request in its URL. There is a special file, called partitions.xml, which specifies two configuration lists: expressions and partitions. The expression list consists of all regular expressions that will be used to extract valid partition names from incoming HTTP requests. The partitions list contains all valid partition names identifying all partitions that should be managed by XD and activated in back-end target servers.
For existing applications the deployment specialist must find some constant and recurring information in each HTTP request to construct a partition name. For new applications the partition name can be designed into the HTTP request.
The scenario described in the next section uses HTTP partitioning, where partitions are defined using the URL of an HTTP request.
| Note: In order for an application to be recognized as partitioned, it must contain a Partitioned Stateless Session Bean (PSSB). A PSSB is a stateless session bean that implements the PartitionHandlerLocal interface, and can utilize the PartitionManager to create partitions from the WPF framework. A PSSB must be introduced into the WebSphere Commerce EAR as a prerequisite to partitioning it. You can find more information about the PSSB and the PartitionHandlerLocal interface in the XD references listed at the end of this appendix. |