[OT] How to deploy a new version of a webapp on a cluster

[János Löbb <ja...@yale.edu>]

Hi,

Let say there is a webapp called mywebapp on a two member tomcat cluster.  Let's call the members tomcatA and tomcatB.  The Developer wants to deploy a new version of mywebapp.  The following procedure was thought:
	-	Shut down one of the tomcats.  Let it be tomcatA.  From here on the existing sessions will be served from tomcatB till further notice.
	-	Replace the clustered server.xml on tomcatA with a non-clustered server.xml
	-	Bring up tomcatA.  At this moment tomcatA is not participating in the cluster, any session with the URL: http://hostA:8080/mywebapp should have a standalone session id with no indication any of the two tomcat instances.
	-	Undeploy mywebapp.
	-	Deploy the new mywebapp on tomcatA with the olld name, that is as mywebapp.
	-	Shut down tomcatA
	-	Replace the non-clustered server.xml with the clustered server.xml
	-	Startup tomcatA

Here is the point where I need guidance.
	-	Does the tomcat cluster know that mywebapp on tomcatA is different from mywebapp still running on tomcatB ?  If yes, how does it know it ?  Will at this point the sessions from tomcatB replicated to tomcatA ?  
	-	If I want my new mywebabb to clusterized should I deploy it also on tomcatB ?  If yes - because somehow the cluster knows that although the name and the context path is the same, the apps are in reality different -, then how,t do so and at the same time preserve the existing sessions in tomcatB, that is replicating them over to tomcatA.

My test shows, that if I just start up tomcatA with the new mywebapp on it as soon as I shut down tomcatB the sessions over tomcatB are lost.  I would like to preserve those sessions and bring them over to tomcatA, so I can do the same procedure on tomcatB that I did on tomcatA, that is replacing the old app with the new one.

So I am interested how others are doing it without loosing any sessions and without restrictions t the users.

Thanks ahead,

János
	
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