Re: Cluster Sendmail?

[Ed Wilts <ewilts ewilts org>]

On Wed, May 18, 2005 at 11:39:15AM +0100, John Haxby wrote:
> Christopher McCrory wrote:
> 
> >On Wed, 2005-05-18 at 12:45 +0300, Jussi Silvennoinen wrote:
> > 
> >
> >>>IMHO, you don't need HA  Cluster for building HA sendmail solution -
> >>>using several MX records with the same priority is enough.
> >>>     
> >Multiple A records might work
> >
> >mail.outgoing IN A 172.31.31.1
> >             IN A 172.31.31.2
> >             IN A 172.31.31.3
> >             IN A 172.31.31.4

In practise, this is working very well for us.

> That's all fine and dandy provided none of the mail.outgoing machines 
> has the termerity to crash while there is mail in its mail queue.

If the mail is in its queue but not yet delivered, it will go out when
the system comes back.  If it doesn't come back, then you've got a
problem.  However, unless your cluster solution has a cluster-wide mail
queue, you'll have the same issue.

> Multiple A records do load balancing to a certain extent (DNS round 
> robin) but as Jussi has just pointed out, the abiliy of some MUAs to 
> deal with multiple IP addresses for one name is, shall we say, lacking 
> which makes them pretty well useless for availability.

As I've said, this isn't a problem for us in practise.  Even with the
nasty Exchange as one of the main mail generators.

> Anyway, neither are any good for HA unless you can guarantee that a 
> machine will only crash when its mail queue is empty :-)

My mail systems (Red Hat Linux 6.x) don't crash :-).  Seriously, they've
never, ever crashed.  We had a data center power outage a couple of
times but the server came back and processed its mail queue.

-- 
Ed Wilts, RHCE
Mounds View, MN, USA
mailto:ewilts ewilts org
Member #1, Red Hat Community Ambassador Program