[BlueOnyx:05260] Re: Secondary mail server

[Gary Sedgwick]

Hi Chris,

Many thanks for all the info.  I'd appreaciate it though if you could
explain what exactly would happen in the scenario I described, and why
mail will "randomly" end up on each server.

When I say the two boxes will be configured identically, I meant in terms
of vsites/users.  The DNS would be unique for each though, with the high
priority MX record pointing to the main mail server for each domain, and a
lower priority MX record pointing to the server configured as "secondary
mail server".  I'm hoping the mail would always end up at the primary
server (and hence the mailboxes) in this scenario due to using the higher
priority MX record, and only at the secondary server if the main one is
unreachable.  The question is, what happens on the secondary server - does
it queue up, or deliver to mailboxes, if vsites/users are set up as well
as the secondary mail server setting?

I've done a lot of investigation into various things like
heartbeat/DRBD/pacemaker/haproxy/GFS/RHCS.  My feeling at the moment is
that, for what I'm trying to achieve, heartbeat/pacemaker is just too
complicated (to do correctly anyway i.e. with STONITH etc.), GFS is
incompatible with BlueOnyx due to requirement for ext3, and DRBD is great
but limited to primary/secondary without GFS or similar.  My requirements
are that I need swift failover of Apache (hence haproxy and active/active
type config), but only need to make sure mails are not lost (so
active/passive type config, but with secondary mail server running to make
sure mails aren't lost) in regards to e-mail.  I'm pretty confident this
is the way I want to go, I'm just not sure about how the secondary mail
server setting in BX interacts with already configured vsites/users.

Gary

> Hi Gary,
> Be very, very careful with your configuration.  Long story short,
> though, you can save yourself the trouble of setting up another box to
> test with.
>
>> If two BlueOnyx environments are set up with the same domains/vsites and
>> users (but different IPs obviously), but I configure the Secondary Mail
>> Server in one to point to the other, will that take precedence over the
>> usual mailbox delivery on that particular server (in the case the other
>> one is down)?
>
> This is NOT how it works.  If you just configure 2 BX boxes, then they
> will both just assume that they are authoritative for the domain.  You
> can configure one as a primary and one as a secondary MX if you want,
> but that won't really do what you're thinking it will, either.  What
> you'll wind up with is mail "randomly" ending up on one box or the other.
>
>> I'm thinking about loading two servers from the same
>> cmuexport, and using them for load balanced web serving, but just having
>> mail delivered to one box with the other available as a backup mail
>> server
>
> Save yourself time and trouble.  Don't do it.  Rather than putting up 2
> servers for "load balanced web serving", just put up one server that's
> robust enough to handle the load.  If the site is busy / important, make
> sure you're not hanging a monster server off a DSL or T1 line and put it
>   with a facility that is robust enough to support the traffic.  It
> always amuses me when folks put in monster dual-quad core servers with
> 12GB RAM so they can do their own server on a DSL line.  Whoops!
>
> But back to point, what will wind up happening, again, is that you'll
> have email going "randomly" to both servers that you've set up.  In
> addition, assuming you're using round-robin DNS to resolve your WWW to
> either server, you're going to have inconsistent logging, sessions that
> don't carry across and databases that are not synced up.
>
> If you want to use 2 servers for redundancy, then configure them in a
> cluster.  Aventurin{e} makes this drop-dead simple.  Or you could roll
> your own cluster using Linux heartbeat clustering, some rsync and some
> MySQL replication.   I've worked both ways.  For my time and money,
> Aventurin{e} is the way to go.  You just set it up and it works.
>
>> - I'm guessing sendmail will end up with configuration for the vsites as
>> well as the secondary mail server, but in the event of the main server
>> failing will mail queue up waiting to be delivered to the main server
>> (as
>> I'm hoping), or will it be delivered to the redundant mailboxes on the
>> secondary server?
>
> Yes, I can see how you'd guess this but it isn't at all the way it will
> work out.   Just setting up another server with an identical
> configuration will not give you the redundancy you're looking for.  It
> will give you headaches and heartbreak.
>
> So by now you're asking "so what's that secondary mailserver box for if
> it doesn't do what I want?"   Ah.   Happy to explain.
>
> What it's there for is in the event that you want to set up a secondary
> server that will queue your inbound email in the event that your primary
> system goes offline.  The idea would be that the secondary box will
> accept the email then queue it for delivery to your primary system as
> soon as it becomes available again.  That way nobody loses email during,
> say, a reboot or when the DSL line you're hosting your dual-quad
> mega-RAM, RAID-10 box peters out on you only to return whenever the
> telco gets around to it.   :)
>
> I hope that helps sort it out for you.
>
> --
> Chris Gebhardt
> VIRTBIZ Internet Services
> Access, Web Hosting, Colocation, Dedicated
> www.virtbiz.com | toll-free (866) 4 VIRTBIZ
>