Re: question about using MX's for load balancing

To: tc lewis <tcl@xxxxxxxxx>
Subject: Re: question about using MX's for load balancing
Cc: lvs-users@xxxxxxxxxxxxxxxxxxxxxx
From: Jeremy Hansen <jeremy@xxxxxxxxxxxxx>
Date: Thu, 30 Mar 2000 17:53:18 -0500 (EST)
This I don't know, but as I understand it, remote mail targetted for the
primary is held on the secondary only until the primary becomes available
again and the secondary host is only queues the mail.  If you can get a
secondary machine to just go ahead a deliver the mail, then this whole
this would be a non issue, this is what I don't know.

>From what I see on the qmail based machines here is that the secondary
only hold the mail and is retried with the same interval as a regular
deferred message.


> can't the secondary mx be configured to simply deliver the mail as the
> primary would?  in which case there would be no delay...
> -tcl.
> On Thu, 30 Mar 2000, Jeremy Hansen wrote:
> > 
> > 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.
> > 
> > Thanks
> > -jeremy
> > 
> > 
> > 
> > 
> > 
> | jeremy@xxxxxxxxxxxx

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