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From "William A. Rowe, Jr." <wr...@rowe-clan.net>
Subject Re: [users@httpd] Re: Newbie Qu - details of graceful restart on Windows
Date Tue, 07 Jun 2005 16:43:03 GMT
At 01:17 PM 6/6/2005, dhay@lexmark.com wrote:

>>>My main concern is whether its possible for requests to be dropped during
>>>this process, and whether session affinity is maintained - eg if a
>browser
>>>is already talking to a certain Tomcat, will it continue to talk to
>exactly
>>>that one after the restart?
>
>> Of course not, when you talk about a 'browser talking to Apache'
>> this usually consists of many separate requests, one after another
>> (and sometimes in parallel.)  The next request initiated after the
>> graceful restart will speak to a new Apache instance.

>Ummm...do you mean a browser talking to Apache or Tomcat?  I understand
>that the next request will speak to a new Apache instance, but I would have
>thought (hoped!) that session affinity would have been preserved across the
>restart and the browser would still talk to the same Tomcat.  Can I clarify
>that you are saying that this is *NOT* the case?

First, you are really off to the subject of Tomcat which is better
addressed on the Tomcat users forum.  But to make the long story
(which you can ask at that list) much shorter;

If your Apache is configured with ajp13 to speak to a backend Tomcat,
and you DON'T restart Tomcat, then session affinities created by Tomcat 
would be retained, because there is only one Tomcat server.  If you
are speaking to a cluster of Tomcat servers, additional session state
configuration is required in Tomcat.

It's also possible to use mod_unique_id or similar Apache-side session
state management, which could become confused by switching between 
Apache generations, depending on exactly how things were configured.
That's left as an exercise for the reader.

Bill



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