The on demand router (ODR) is an intelligent HTTP and Session Initiation Protocol (SIP) proxy server in WebSphere® Virtual Enterprise. 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. You can configure the ODR to determine how it handles failure scenarios and how it tunes certain work requests.
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 through starting/initializing. If the application is started on other application server(s), then the requests will be routed to them. If the application is not started on any other servers, then the ODR will still not route to the starting-in-progress application server. Instead, a 503 is returned.