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From Jeffrey Janner <Jeffrey.Jan...@PolyDyne.com>
Subject RE: mod_jk Avoid loadbalancing
Date Wed, 16 Nov 2011 17:46:51 GMT
> -----Original Message-----
> From: Pid [mailto:pid@pidster.com]
> Sent: Tuesday, November 15, 2011 9:09 AM
> To: Tomcat Users List
> Subject: Re: mod_jk Avoid loadbalancing
> 
> On 15/11/2011 15:00, Jeffrey Janner wrote:
> > Alexander -
> > From reading your emails, it sounds like you have the following setup
> >
> >                        F5 HW-balancer
> >                              |
> >                             / \
> >                            /   \     Level 1 balancing
> >                           /     \
> >                        HTTPD1  HTTPD2
> >                           |      |
> >                      ----------------   Level 2 balancing
> >                      |       |      |
> >                     TC1     TC2    TC3
> >
> > Is that correct?
> > You state that you want to eliminate Level 2.
> > However, from a performance standpoint, why would you?  Without the
> Level 2 balancing, it is conceivable that one of the 3 Tomcats could
> end up processing the bulk the JSP requests.
> 
> Why?
> 
> 
> p
To be honest, I don't think you can set up the Level 2 without some form of load-balancing,
even if it is just round-robin.  But perhaps I'm not processing the full impact of how the
whole structure will work, considering the OP wanted to eliminate the Level 2 LB.
I would think one would want the F5 to balance the loads on the HTTPD servers for that traffic,
and let the HTTPD servers decide best use of the Tomcats to avoid overloading one (reason
for LB).  Since the OP hasn't bothered to provide his physical or logical layout and his exact
goals, I was postulating on theory alone.
However, his subsequent response makes it sound like he has 3 systems with HTTPD & Tomcat
on each system.  It sounds like what he really wants is for HTTPD to forward only to Tomcat
on the same server and let the F5 load balance and failover that setup.  Sounds reasonable,
and fairly easy to set up.  However, if he wants the above LOGICAL setup, then he needs to
rethink his architecture.  For example, my suggestion at the beginning of this paragraph won't
handle failover where only the Tomcat on server1 goes down, but the HTTPD is active.  Configuring
for that eventuality takes a little more thought.  I've not done enough playing with the mod_jk
config to be sure that is possible, but no one who is has weighed in on the specifics of his
problem, probably because he hasn't fully explained the scenario he is trying to implement.
Jeff
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