Creating and configuring ODRs

The on demand router (ODR) is an intelligent HTTP and Session Initiation Protocol (SIP) proxy server in WebSphere® Virtual Enterprise. You can configure the ODR to determine how it handles failure scenarios and how it tunes certain work requests. The ODR is the point of entry into a WebSphere Virtual Enterprise environment and is a gateway through which HTTP requests and Session Initiation Protocol (SIP) messages flow to back-end application servers.

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The ODR can momentarily queue requests for less important applications in order to allow requests from more important applications to be handled more quickly or to protect back-end application servers from being overloaded. The ODR is aware of the current location of a dynamic cluster instance, so that requests can be routed to the correct endpoint. The ODR can also dynamically adjust the amount of traffic sent to each individual server instance based on process utilization and response times. By default, the ODR binds to ports 80 and 443 for listening on HTTP and HTTPs, which requires running the ODR as a root user. If you want to run the ODR as a non-root user, you must change the PROXY listening ports to values greater then 1024.

The ODR is fully aware of the dynamic state of the cell, so that if one server in the cell fails, the requests are routed to another server. When the ODR is notified that the application has initialized on the restarted server, the ODR will route requests to that server again.

The ODR will not route any requests to the application on the application server until the application is started. If the application is started on other application servers, the requests will be routed to them. If the application is not started on any other servers, the ODR will still not route to the starting-in-progress application server. Instead, a 503 is returned.


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