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From Rainer Jung <>
Subject Re: JK Sticky Session Handling with Load Balancing
Date Tue, 18 Apr 2006 13:29:21 GMT

1) If you want to use a mod_jk lb worker with sticky sessions, you need 
three ingrediants:

a) configured lb worker with sticky_session (default is 1=on) and a 
corresponding JkMount to this lb worker

b) tomcat instances with unique jvmRoute settings in server.xml (the 
jvmRoute gives each instance its name) and worker configurations for the 
balanced workers where the workers names are equal to the jvmRoutes and 
host/port are correct for the repective tomcat instances

c) Correct configuration of URL encoding or usage of session cookies in 
the target tomcat instances.

If these three conitions are met, then it works like that:

- Any request without cookie or URL encoding will go to one of your 
tomcat instances. Which one depends on subtle load balancing decisions.

- Any request without cookie/encoding received by a tomcat instance will 
return a response with a JSESSIONID-cookie or URL encoding of all 
embedded links (assuming c)). The cookie resp. URL encoding will end in 
a dot "." appended with the jvmRoute of the tomcat instance.

- Following requests with cookie or URL will be processed by the lb as 
follows: It will search for a dot '.' in the cookie (with name 
JSESSIONID) resp. in the URL part ";jsessionid=". Then it will take the 
string after the dot and look in it's balanced worker table, if it can 
find a worker with the same name that is not in error state and then 
will send the request there. In case no such worker exists, it will 
handle the request like in the first case.

Allistair Crossley wrote:
> Hi Edgar,
> Yep I just noticed that too :)) However, correcting this configuration
> (to the below) does nothing to resolve the issue, because the lb worker
> type by default has sticky_session=1. I set it explicitly anyway as
> below.
> However, I have noticed that in fact Tomcat 2 is not returning
> JSESSIONID headers as Tomcat 1 does when both Tomcats are in.
> To recap then, when only Tomcat 1 is in the loop, JSESSIONIDs are
> returned and remains consistent across requests. When Tomcat 2 is
> brought in, Tomcat 1 starts generating a different JSESSIONID per
> request, whilst Tomcat 2 returns no JSESSIONID at all.
> Thanks, Allistair
> === new config ===
> worker.list=loadbalancer
> worker.tomcat1.port=8009
> worker.tomcat1.type=ajp13
> worker.tomcat1.lbfactor=1
> worker.tomcat1.cachesize=10
> worker.tomcat2.port=8109
> worker.tomcat2.type=ajp13
> worker.tomcat2.lbfactor=1
> worker.tomcat2.cachesize=10
> worker.loadbalancer.type=lb
> worker.loadbalancer.balance_workers=tomcat1,tomcat2
> worker.loadbalancer.sticky_session=1
> -----Original Message-----
> From: Edgar Alves [] 
> Sent: 18 April 2006 12:32
> To: Tomcat Users List
> Subject: Re: JK Sticky Session Handling with Load Balancing
> Hi there,
>   You're setting the sticky_session property for each worker. That's not
> how it works.
>   That property is valid only for the loadbalancer and it takes a
> boolean value. Set it to 'True' or '1' to get the desired effect.
>   Read for
> more info.
>   -- Edgar Alves
> Allistair Crossley wrote:
>>I have setup 2 Tomcats on the same machine fronted by IIS, and used a
>>sticky_session=1 JK (1.2.15) load-balanced setup (as printed at the 
>>foot of this email)
>>I setup a JSP on both Tomcats that outputs the session ID.
>>With only 1 Tomcat started, making requests to the JSP results in the 
>>same session ID being output on each request.
>>When I start up the 2nd Tomcat and continue making requests to the 
>>JSP, I am switched between both Tomcats rather than staying on the 
>>same Tomcat and therefore acquire a new session ID.
>>However, with the 2 Tomcat's "in the loop" the session Ids become 
>>different *per request* no matter which Tomcat is used.
>>I would have expected at most 2 unique session Ids (one per Tomcat) 
>>since with 1 Tomcat running only, the 1 unique session ID is
> maintained.
>>I would appreciate any help or guidance as to why this may be
> happening.
>>Cookies are enabled, and jsessionid is not being used on URLs.
>>Cheers, Allistair.
>>== config ==
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