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From Emilio Recio <>
Subject Re: Sticky session and ModJK Load Balancer
Date Mon, 06 Jul 2009 18:27:14 GMT
Mark Thomas wrote:
> Emilio Recio wrote:
>> Hi,
>> i have installed Apache 2.2 and two Tomcat 6 whit load balancing in
>> cluster mode using "mod_jk" module and setting sticky session in TRUE,
>> and memory replication. I was testing my project and work perfect.
>> We have a dilemma using sticky session or not using it, with my team work.
>> Setting sticky-session in TRUE, it works fine, even when one tomcat
>> fails-over. When set to FALSE i can see that the session have some data
>> loss, and the project start to fail.
>> I was reading the book Professional Apache Tomcat 6, goggle searches and
>> all kind of information in the net. The recommendation is: use
>> sticky-session in TRUE with memory replication.
>> Nobody mention concrete arguments, and need that to make a report to the
>> system administrator, to make him understand why we need to use
>> sticky-session in TRUE.
> I would have thought the occasional data loss you see is argument
> enough. What more were you looking for?
> Mark
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Hi Mark,
We are developing an e-commerce app. The application store  in session a 
lot of information like user data, user history data, etc.
The scenario is: 3 PC's, one with Apache 2.2, and the others have Tomcat 
6. Apache has mod_jk to make load balancing, and the Tomcat 6 have 
configured in memory session replication, to support fail-over.
    Some times: Tomcat1 after the login, has all the user info charged 
in session, when load balancer try to use the Tomcat2 some info is saved 
but other info is missing.
We need to know good arguments to justify to the client, why we should 
use sticky session in true to avoid this missing data issue. The client 
doesn't want to use sticky session in TRUE, they arguments are: "We 
loose performance in transactions and loose of loadbalancing (using 
sticky session in TRUE). Using sticky session in FALSE the Tomcat more 
idle attend the request that incoming and gain performance. One example: 
You have 4 users, two in tomcat1 and the other two in tomcat2. If users 
in tomcat2 logout, this stay idle when the other is attending the other 
two users. So, you "loose load balancing"."

They arguments are partial true, using stick-session in TRUE , you have 
one tomcat attending a client session during its life cycle; even if 
this users are idle or has very active session. Its stable and fail-over 
tolerant. Of course you "loose" performance.
So we need good arguments to explain why we need use, sticky session in 
My regards,
    Emilio  Recio

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