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From Gal Robert <>
Subject Re: Silent runtime replace of a class
Date Tue, 05 Jul 2005 17:07:47 GMT
I'll give you the user- requirement, to understand better the problem:
"pre-defined subsystems or modules should be upgraded or patched without 
interfering/interrupting system usage (defined by the supplier)".

Often happens, that we must correct a little error in business logic.
In these cases we usually patch a class file, and replace it in the 
application, then redeploy it.
 From your (and other) responses it seems, there's no correct way to
do such a patch without redeploying the application.

On the other hand, your idea about tomcat clustering, and redirecting 
requests sounds quite interesting. I think, this would satisfy the above
requirement. Can you give me some more information about your idea? Does 
it require a deep know-how?

thank you and others

Peter Crowther wrote:
>>From: Sriram N [] 
>>--- Gal Robert <> wrote:
>>>we have a new user requriement: to be able to modifiy the 
>>>application without affecting user work.
> That's a very broad requirement, and may not be achievable in its full
> form.  Does this mean that users must be able to continue working while
> a new version is deployed, unaware that a new version is being deployed
> under their feet, keeping all session context and so on?  If so, I think
> you're onto a loser unless you can cluster your Tomcat instances - at
> which point you can point all your users to one of your instances (call
> it instance1) until there are none on instance2, upgrade instance2,
> point new users to instance2 until there are none on instance1, upgrade
> instance1, then go back to using both instances if you wish.
> This requires other software or hardware to keep track of which user
> sessions are using which instance.
>>You'll could place the context.xml in either the conf 
>>directory, or in the
>>war's WEB-INF folder. Just ensure that the "reloadable" 
>>attribute is set to "true".
> Note that reloading a webapp when you have made changes may not allow
> the user to continue working - for example, if you've changed what's in
> the session then they may get errors.
> 		- Peter
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