WebSphere Virtual Enterprise, Version 6.1.1
             Operating Systems: AIX, HP-UX, Linux, Solaris, Windows, z/OS


Cell affinity when an ODR fails

The cell affinity function enables you to configure unbridged, multi-cell, on demand router (ODR) topologies that preserve sessions even in the event of ODR outages. This topology diagram shows the cell affinity request/response flow when an IBM HTTP server request must be sent to an ODR which is not on the original session path, because the original ODR has become non-functional

A scenario featuring a request/response flow is shown in the following diagram. In this scenario, the browser has sent an in-session request to the IBM HTTP server. The IBM HTTP server has determined it cannot forward the request to the original ODR 1.1, so it has chosen to forward the request to ODR 2.1 instead (normally, this would break the session). The solid arrows in the diagram represent requests, whereas the broken arrows represent responses. The flows are explained below in the following sequence:
  1. The browser sends a request to IBM HTTP server. ODR1.1 is not functioning. In an attempt to failover, IBM HTTP Server routes to ODR2.1.
  2. ODR2.1 notes that the request was originally destined for ODR1.1, so ODR2.1 finds a generic server cluster generic server cluster containing ODR 1.1, and routes back to an active ODR within the generic server cluster, namely. ODR 1.2.
  3. ODR1.2 marks this session for adoption during response processing and forwards the request to the original back-end target cluster.

The IBM HTTP server could route directly to ODR 1.2 after detecting that ODR 1.1 failed. In this case, ODR 1.2 would forward the request to the correct back-end target cluster and adopts the session during response processing as described in #3 and #4 previously.

The following diagram illustrates a request/response flow scenario in which a browser sends an in-session request to the IBM HTTP Server.


Single ODR failure




Related information
Enabling cell affinity
Configuring cell affinity in a multi-tiered environment
Defining generic server clusters for remote ODR cells
pluginMergebat|.sh script
Creating and configuring ODRs
Configuring ODRs
Concept topic    

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Last updated: Oct 30, 2009 1:32:42 PM EDT
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