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From "Len Popp" <>
Subject Re: Are Sticky Sessions really necessary?
Date Fri, 02 Nov 2007 21:37:25 GMT
You can indeed use session replication without sticky sessions, and
the session data will be copied to all the Tomcat servers. However it
may be inefficient. You probably have to use synchronous replication
to ensure the session data is consistent across the cluster, which
adds latency to the requests. And there could be a lot of extra
network traffic in the cluster if it's busy (which it is, otherwise
you wouldn't be doing load balancing).

(I haven't used session replication in a high-load situation. Maybe
someone else can tell us how well it works.)

On 11/2/07, Stephen Wick <> wrote:
> The Tomcat 5.5 "Clustering/Session Replication Guide" says, "Make sure
> that your loadbalancer is configured for sticky session mode."  However,
> I don't see the term "Sticky" sessions anywhere in the Servlet 2.3 or
> 2.4 specifications.
> Are sticky sessions really required for clustering to function properly
> in Tomcat 5.5?  I thought that session replication would eliminate any
> need to direct a client session to one node in a cluster.
> If not, can we adjust the documentation to indicate that Sticky sessions
> are optional, for the appropriate reason (I'm guessing the advent of
> session replication in tomcat.)
> I am asking this question because I am having trouble with Sticky
> sessions in my load balancer, and I need to know whether or not I should
> pursue fixing this feature.  If tomcat doesn't really require sticky
> sessions, then I can leave my load balancer alone.  If tomcat does need
> the feature to function properly, then I need to go to some additional
> expense to resolve the issue with my load balancing appliance.
> Thank you for your time and expertise.
> Stephen Wick
> Interactive Developer
> Nicholson Kovac, Inc.
> References

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