FAQ
Hi Jorge, thanks for the reply.

Actually no, these are the access logs from the Tomcat cluster members;
you can view the corresponding AccessLogValve entries in the server.xml
files referenced below.

I included those logs for illustration, but I have confirmed that those
are the actual session IDs at the browser. After the failover the new
Tomcat cluster member sends a new Set-Cookie header with the new session ID.

You're right that the first portion of the session ID does seem to be
replicated properly, but I thought it was the function of
JvmRouteBinderValve to update the entire session ID in a failover,
including the jvmRoute portion.

Best wishes,
Roy

Jorge Medina wrote:
Are your logs Apache logs? Mod_jk logs?

If it is Apache, the question would probably better answer in the Apache
mailing list.
Anyway, What does your LogFormat string looks like?

I bet what you see in the logs is the concatenation of the session ID
and the worker name. I doubt two servers would generate the same hex
digits for the session. Therefore, your server must be working as
expected, you are just interpreting the logs incorrectly.

-----Original Message-----
From: Roy McMorran
Sent: Thursday, April 02, 2009 10:59 AM
To: Tomcat Users List
Subject: Session Replication in Cluster

Hello all,


I've built a very simple 2-member Tomcat cluster for testing, but I am
unable to get the session replication quite right. The problem is when
I fail one member of the cluster. The behavior I was expecting is that
the other cluster member would take over the session ids for the failed
member. However it is appending it's own jvmRoute value to the session
id, and thus setting a new cookie.


Details:
I have 2 cluster members, "itchy" and "scratchy", running on the same
physical server, and CATALINA_BASE is /var/tomcat/itchy and
/var/tomcat/scratchy respectively. Tomcat 6.0.18 binaries, etc. are at
/usr/local/tomcat. Using mod_jk 1.2.27 on Apache 2.2.11 (Apache is also
on the same server). I am using sticky sessions.


Here are the access logs for the 2 members from a short "failover"
experiment (note I'm including the session ID in the 2nd field). The
session starts on scratchy. From scratchy_access_log.2009-04-02.txt:

192.168.200.177 E5BF3FFA9AEE1E3AB0DD4A96BA5E4011.scratchy -
[02/Apr/2009:10:19:55 -0400] "GET / HTTP/1.1" 200 14612
192.168.200.177 E5BF3FFA9AEE1E3AB0DD4A96BA5E4011.scratchy -
[02/Apr/2009:10:20:14 -0400] "GET /about/ HTTP/1.1" 200 19507


At 10:21:39 AM I do a kill -9 on the scratchy instance. Now the traffic
goes to the other cluster member as expected. From
itchy_access_log.2009-04-02.txt:

192.168.200.177 E5BF3FFA9AEE1E3AB0DD4A96BA5E4011.itchy -
[02/Apr/2009:10:22:11 -0400] "GET /about/publications/ HTTP/1.1" 200
18263
192.168.200.177 E5BF3FFA9AEE1E3AB0DD4A96BA5E4011.itchy -
[02/Apr/2009:10:22:32 -0400] "GET /about/changes/ HTTP/1.1" 200 12736


Note however that the new member's jvmRoute value is now appended to the
session id. I thought is was supposed to stay exactly the same after
failover.


Additional details can be found as follows:

server.xml for "itchy" - see:
http://gillnet.mdibl.org/~mcmorran/itchy-server.xml.txt

server.xml for "scratchy" - see:
http://gillnet.mdibl.org/~mcmorran/scratchy-server.xml.txt

context.xml (identical) - see:
https://gillnet.mdibl.org/~mcmorran/context.xml.txt

workers.properties:
https://gillnet.mdibl.org/~mcmorran/workers.properties

I've also included the catalina.out file for both, from startup and
through the test at:
https://gillnet.mdibl.org/~mcmorran/itchy-catalina.out
https://gillnet.mdibl.org/~mcmorran/scratchy-catalina.out


I'd appreciate any advice on where I went wrong. Thanks and best
wishes,
Roy

--
Roy McMorran
Systems Administrator
MDI Biological Laboratory
mcmorran@mdibl.org



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