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From "Nick Bauman" <>
Subject Re: FW: [advanced-servlets] Session Load Balancing (was: To avoid
Date Wed, 28 Feb 2001 04:55:51 GMT

> Yes, and the way I've seen people solve this issue is to make each
> server constantly replicate its sessions to another server so that any
> session's state is stored in two servers (not just one).  For example,
> if you've got four servers, A, B, C, and D, you configure A to
> replicate to B, B to replicate to C, C to replicate to D, and D to
> replicate to A.  Then the "composite ID" would contain the primary
> server tag, secondary server tag, and the session ID, like: 
> A:B:sessionXXX.  So, if server A went down, the load balancer could
> still get session info from server B, and at the  same
> time let server D know that A is down and to replicate to B until
> further notice.


This is once again only making sure a majority of the sessions are saved in
a rotation. A lot of work for very little real fault tolerance.

Also I think your english up there indicates a solution that causes
tremendous hysterysis amongst the servers.

> This also works when each server replicates sessions to more than one
> backup server so that you've got even higher fault tolerance (but
> you'll probably never need that level of fault tolerance).

Now you may have something: a seperate, parallel, session cluster.

> -- 
> Jason Brittain

Nick Bauman

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