Sticky Sessions and Windows Azure

Richard Astbury's Blog

One of the problems that often crops up with moving legacy applications to the cloud is reliance of sticky sessions. The Azure load balancer works on a round-robin basis, so if your application has been designed to work on a sticky session basis, you may have some work to do.

Although it is possible to use Sticky Sessions in Azure (see this example) it’s not a great fit for cloud architecture, for these reasons:

  1. When you provision new instances, only new sessions will be routed to them. Depending on your load balancing logic, new sessions may also still be provisioned on the old instances. This results in it taking a long time (depending on the average length of your session) for load to be evenly distributed across your instances.
  2. Cloud solutions should be designed to fail. One of your instances may be removed at any time for patching…

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