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From gaston.aze...@free.fr
Subject Re: [Tomcat] Looking ofr JSESSIONID in Tomcat
Date Mon, 31 Jul 2006 09:15:42 GMT


Thanks a lot, Christopher, for your answer, but I am looking for a solution the
most generalizable possible. Does it exist an interface or a Mbean in Tomcat
responsible for managing the session (and so my cookie JSESSIONID)?

Thomas

PS: I am currently looking for a Tomcat's test where the developers may have
tested the behavior of the cookie/session.

Thomas,

>> My current work relates to a context where we want to update a J2EE
application
>> without stopping it.

>Well, you'll certainly have to stop the application at some point. I assume you
mean that you don't want a complete cut-over to the new system: you need a hased
cut-over to assure continuous uptime.

> The general process is to do the following:

> 1. Wean users off some of your production servers. This can usually
>   be done by removing those servers from the load balancing or DNS
>   rotation.
> 2. Wait for #1 to complete (usually a period of a few hours or even a
>   day or so).
> 3. Bring your new servers online, and switch the load balancing or DNS
>   rotation completely over to the new servers. Allow your load balancer
>   to continue to route "old" sessions to the servers running the old
>   version.
> 4. Wait for all sessions to die on the "old" servers.
> 5. Upgrade the remaining servers and reset your load balancer to use
>   all servers.

>> As a result we have to separate both, this separation is possible because of
>>the
>> use of the cookie JSESSIONID.
>>
>> I have modified a load balancer (mod_jk) to do this, but when the load
>>balancer
>> receives a HTTP request it can't know whether the session is always available
>> or not (Indeed a session may expire and the cookie bind to it becomes
>>invalid).
>
>> So I want to know if it is possible for an external program to test if a
>>session
>> exists on the Tomcat server? Or what is the name of the structure/object
>> managing Tomcat's cookies in a cluster? Or how does Tomcat make to know if
>> cookie is valid?

> There is at least a cheap way of doing this: make a request to the
> server to some protected URL, and include the session id as a parameter
> instead of a cookie. Something like this:

> http://your.server/protected/url;jsessionid=[SESSIONID]

If you get a challenge for a login, then the session does not exist.

> This doesn't sound like a really good solution, though. Your better bet
> is to use a load balancer that can set an app server affinity and keep
> track of that (usually using a cookie). Then, you blindly forward
> requests to the server to which the session was previously assigned.

> -chris

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