question about using MX's for load balancing

To: lvs-users@xxxxxxxxxxxxxxxxxxxxxx
Subject: question about using MX's for load balancing
From: Jeremy Hansen <jeremy@xxxxxxxxxxxxx>
Date: Thu, 30 Mar 2000 17:24:38 -0500 (EST)
Basically I want some pros and cons on using MX's for load balancing mail
hosts.  I know this doesn't seem to be LVS related, but it is because I'm
currently using LVS for this operation and it's working perfectly, but
someone I met with yesterday is using another method, MX's with the same
priority to basically do the same thing, when he mentioned this it didn't
sit well with me for some reason but I couldn't put my finger on why and
mainly I think it has to do with fail over incase one of these MX hosts
are down.

In our particular situation our goal is high volume mail.  The goal is to
get as much mail out as fast as possible.

In a MX load balancing situation, it seems to me that although it may
work, it's not as efficient in the goal incase a machine is failed.

This is my understand on how it would work using MX's.  If whatever dns
determines to be the target host, if the host is failed, then the mail get
deferred to a secondary MX host and is held until the original targeted MX
host is back up then the secondary pushes that mail back to the original
target.  So mail is deferred and delayed.  Will this be the case even if
the MX priorities are the same?  I'm assuming once an MTA determines which
host it decided to go to, this address doesn't change even with the same
priority levels.

In an LVS situation (assuming you have a good setup and monitoring to take
downed hosts out of the LVS pool) this wouldn't happen.  You hit the
virtual address and it goes to a valid "up" machine and there is no delay.

So LVS still seems better, but I wanted to ask others incase my
assumptions are wrong.


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