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List:       haproxy
Subject:    Re: Custom load balancing logic
From:       Willy Tarreau <w () 1wt ! eu>
Date:       2010-06-27 6:00:00
Message-ID: 20100627060000.GF13151 () 1wt ! eu
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Hi,

On Mon, Jun 21, 2010 at 04:23:32PM +0530, manu tripathi wrote:
> Hi,
> I am a newbie and need to setup a load balancing setup where haproxy will
> distribute load between 2 or 3 tomcats(each tomcat resides on a different
> machine) based on a parameter coming in the URL. Based on that parameter I
> have to carry on some logic and implement an algorithm in java/c and then
> send that request to the corresponding tomcat. Please explain how to do
> that. For eg. I have unique Id coming in as the URL parameter. The tomcat
> installed in each machine has a DB which can only allow a range of that ID.
> So I want to apply the logic on the haproxy (either by some reg ex or
> implementing some load balancing class of haproxy) such that the request
> containing that ID belonging to the particular machine is routed to that
> machine. Please help??

You should take a look at the ACLs in doc. There's a whole set of ACLs
that could be used in your case, most likely url_reg and url_sub which
respectively match a regex and a substring. For instance, it might make
sense to look for substring "id=1" or "id=2" if you know that all IDs
1xxxx or 2xxxx are to be matched.

There's just something unclear in your case, as you're saying that haproxy
will perform the load balancing itself, and later you're saying that you
want to be able to select the server from another place (your "java/c"
which I don't understand where you want to place it). Also, each time you
want to force load balancing decisions, you have to define how you want
the system to behave when the selected server is dead (error, redirect
to another one, etc...). This is very important because it is what
describes what your architecture will look like, and will imply some
major choices for your configuration.

Willy


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