Re: Failing a JK Worker thread

[Dan Thiffault]

We have an application running as a webapp which requires legacy 
systems and network resources which are not fault-tolerant.  Luckily 
these resources are stateless. So we have replicated these resources so 
that one is available per tomcat instance.  When we attempt to use one 
of these resources from within the webapp and it fails, we need a way 
to try the next pair (tomcat &  legacy) in the group.  This will allow 
us to provide a balanced & fault-tolerant service with a webapp 
interface.  Since the tomcat instance is responding and functioning, 
the reply_timeout was not met so apache webserver considered the 
request a success.  Providing a application error from tomcat (maybe a 
503 or 401 instead of 500) seemed like the "rightest" way to do it.

I see a few other options:
1. Put a layer on top of apache that tests the response and makes a new 
request.  This doesn't buy us anything and circumvents the use of jk
2. (some how/maigcally) Send an out of process message from tomcat back 
to apache that the resource is down.
3. Modify AJP to handle this error (this may already have a mechanism 
that I missed)

Does any one have any other suggestions for ensuring reliability when 
there is a 3rd party piece of hardware/software which your webapp 
relies on that has no fault-tolerance of its own?

Thanks for any suggestions,
Dan
On Mar 15, 2005, at 2:50 PM, Guernsey, Byron ((GE Consumer & 
Industrial)) wrote:

What is the situation where you find this useful?
Byron
-----Original Message-----
From: Dan Thiffault [mailto:[EMAIL PROTECTED]
Sent: Tuesday, March 15, 2005 1:41 PM
To: Tomcat Users List
Subject: Re: Failing a JK Worker thread
I didn't hear back from any one so I looked through the code. I couldn't
find any sign of code that would provide this functionality, so I added
the following before line 605 of jk_ajp_common.c.  I recompiled and it
seems to be working as intended so far.
if (d->status=500) {
        jk_log(l, JK_LOG_ERROR,
                "Tomcat server returned status=%d",d->status);
        JK_TRACE_EXIT(l);
        return JK_FALSE;
}
I may end up using a case statement and preventing apache from trying
the next worker on bad request or something like that.  Hope this helps
some one else too.
-Dan Thiffault
On Mar 13, 2005, at 12:01 PM, Dan Thiffault wrote:
I am running apache web server 2.0.49 connected to tomcat 5.0.28 using
the jk connector version 1.2.8.  From my understanding, if I set the
reply_timeout property  of an ajpv13 worker, once the reply_timeout
elapses for a particular request to a worker, apache web server will
make a new request to the next worker in the group.
Is there any way from within the webapp that is being contacted to
induce a failure other than not returning before the reply_timeout? For
instance, can you return an HTTP error message from tomcat that would
cause web server to retry the request to the next worker in the group
(assuming full recovery mode)?
Thanks for any suggestions
-Dan Thiffault
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