[users@httpd] Re: Newbie Qu - details of graceful restart on Windows

["William A. Rowe, Jr." <wr...@rowe-clan.net>]

At 11:38 AM 6/6/2005, dhay@lexmark.com wrote:
>[I asked this on the user list, and think it should have been asked
>here...]

No, it did belong on the users list :)

>I'm quite new to Apache, and trying to understand what a graceful restart
>on Windows actually does.  I'm running Apache with mod_jk with multiple
>Tomcats.  When we add a new Tomcat, I would like to update the
>workers.properties file and then restart Apache so the changes take effect.
>
>Would anybody be able to explain exactly what happens, or point me to
>documentation that already exists?  I've searched the mailing lists and
>googled a lot, with not much detail.

The defintion of graceful means that existing requests are served
out, and when all are finished, that worker process ends.  In the
interim, new worker process(es - 1 on win32) are started to serve
every new incoming request.

>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.

The exception is a keep-alive request.  When Apache is gracefully
restarting, the old process is told to honor no more keep-alive
requests, and terminates the connections after satisfying the next
request.  (It tells the client that the connection will not be 
kept-alive, of course.)

How you configure or restart tomcat on the backend is a different 
issue altogether.

Bill






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