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From Amund Elstad <>
Subject RE: PROPOSAL: mod_jk2: Group/Instance
Date Thu, 02 May 2002 11:41:54 GMT

My understanding of the old lb-worker is that although you can tweak its
behavior using load-balancing factors, it does not theoretically cover:

(1) all requests without a session are routed to a specific tomcat instance
(if that instance is working). 
(2) Tomcat instances in standby or "soft shutdown" mode where they serve
requests bound by established sessions, and requests without a session only
if all non-standby instances have failed.

(1) is (as noted previously) useful when you have a cluster of Apache
(2) is useful in a 24x7 production environment. eg mark an instance for
"soft shutdown", wait for existing sessions to expire, do maintenance
(hardware or software), and then add instance back to normal lb-mode. 

It would be great to have support for both in jk2, for example by using
percentage values for load-balancing factors (adding up to 100% for all
instances in a group). Then, for (1) adjust the lbfactor to 100%, and for
(2) adjust the lbfactor to 0%. 

BTW, I think both the Group/Instance and the Autoconfig proporsals are very
good indeed.

amund wrote:

>On Tue, 30 Apr 2002, Bernd Koecke wrote:
>> some weeks ago I send a patch for mod_jk for an only routing lb_worker. A
>> days later I sent the docu. Henry Gomez said, that it should be commited.
But it 
>> I think it isn't in the repository. But its the same  with me here, to
>> work for to less time :).
>I think it is in mod_jk, I remember seeing the commit. 
>And I think I commited it in jk2 as well ( after some modifications ).
>> I need sticky sessions but no loadbalancing in the module. If a request
>> a session comes in, it should be routed to the _local_ tomcat.
>Well, there is another use-case with the exact same behavior - Apache2 
>with tomcat in JNI mode. All requests without session should be routed to 
>the _jni_ channel ( i.e. in-process, minimal overhead ).
>It's exacly the same - so be sure I do my best to handle this case :-)
>Apache2 acts like a 'natural' load-balancer/fail-over, with the parent
>process monitoring for crashes and it starts/stop childs based on 
>> I think this could be possible with the associated instance of a channel
>> 7). Then I have to configure all four nodes for the same group. Because
>> nodes will serve the same webapps and associate the channel with this
group. But 
>> for this I need a non balancing group. I don't see if the default
behavior of a 
>> group is balancing and if this can be switched off. Is this right or do I
>> something?
>The default is balancing, but you can tune this using weithgs ( and I 
>think we use your code for making one instance 'top priority').
>Please check the code, take a look and send additional comments/patches.
>It's not yet completely done, of course.

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