A Tech Log

November 11, 2008

Sticky Sessions, Load Balancing, Failover and Availability

Filed under: Development,Enterprise & Application Architecture — adallow @ 11:21 am
Tags: ,

All HTTP load balancers support “sticky sessions”: Requests in the same session must be forwarded to the same server node unless there is a failover. You must turn on sticky sessions in your setup. In an ideal world, all nodes in a replicated cluster have the same state; thus, the load balancer can forward any request to any node. But in a real cluster, the network and CPU resources are limited. It takes time to actually replicate the state from node to node. Without sticky sessions, the user gets random HTTP 500 errors when the request hits a node that does not yet have the latest replicated state.

fromjboss doco with some minor editing on my part to keep it just at the concept level.

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