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From André Warnier>
Subject Re: Monitoring Tomcat availability in a load balanced capacity
Date Wed, 12 Nov 2008 21:48:17 GMT
Adam Gordon wrote:
> See my reply to Hassan.  I think setting up a proxy would be overkill, 
> and besides, when running Tomcat in a load-balanced capacity w/ sticky 
> sessions using mod JK, while you can connect directly to the port on 
> which Tomcat is listening for mod JK requests, unless you speak mod JK, 
> it doesn't do anything.

I'm glad there is another solution available directly through mod_jk, 
which I was unaware of.

But re-read my earlier attempt maybe.
I wasn't trying to tell you to talk to the AJP connector from the 
front-end.  I was trying to tell you to talk to Tomcat's HTTP ports, not 
to interfere with the load balancing, which I presume applies only to 
requests coming through the AJP connectors.
Like, at the Apache front-end level :
<Location /tomcat1/are_you_there>
    ---> proxy to http://tomcat1:8080/imthere.html
<Location /tomcat2/are_you_there>
    ---> proxy to http://tomcat2:8081/imtheretoo.html

Seemed pretty clever to me, as a quick solution. ;-)
Maybe due to my lack of knowledge, but I don't really see where the 
overkill would be.

> --adam
> André Warnier wrote:
>> Adam Gordon wrote:
>>> We're running two Tomcat (5.5.16) instances in a load-balanced 
>>> capacity behind an Apache server (2.0.55 w/ mod j/k 1.2.14).
>>> We'd like to set up some sort of monitoring that would allow us to 
>>> not just check to see if the Tomcat Java processes are still running 
>>> (that's easy) but to actually connect to each web server (either 
>>> independently or via the load-balancer) and verify that a certain 
>>> page can be returned.
>>> Since we're connecting to Tomcat via an Apache load-balancer, we 
>>> don't know of a way to force the load-balancer to go to a certain 
>>> Tomcat instance.  Additionally, we don't know how to speak mod j/k so 
>>> we can't fake a direct connection to each Tomcat instance.
>>> Does anyone know of a way or a product (commercial or open-source) to 
>>> achieve this?
>> I don't think you would need a special product to do that, open source 
>> or not.
>> On your Apache front-end, it would probably be easy to set up a proxy, 
>> which via simple HTTP would proxy just the links you want to either 
>> one of your back-end Tomcat HTTP ports.
>> You would need the HTTP Connector active on each Tomcat, but that 
>> should already be the case by default.
>> Someone better versed in Apache mod_proxy could help you there.
>> Maybe try the list at if you don't get more 
>> help here.
>> Of course, if you can access your Tomcats directly through their own 
>> HTTP ports, then you don't even need that.  I'm just assuming you cannot.
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