[Dovecot] nfs director

[Brandon Davidson]

Noel,

On 8/26/10 9:59 PM, "Noel Butler" <noel.butler at ausics.net> wrote:

>> I fail to see advantage if anything it add in more point of failure, with
> 
> i agree with this and it is why we dont use it
> 
> we use dovecots deliver with postfix and have noticed no problems, not
> to say there was none, but if so, we dont notice it.

We might be a slightly larger install than you (60k users, mail on FAS 3170
Metrocluster), but we have noticed corruption issues and the director is
definitely going to see use in our shop. We still use Sendmail+procmail for
delivery, so no issue there... but we've got hordes of IMAP users that will
leave a client running at home, at their desk, on their phone, and then will
use Webmail on their laptop.

Without the director, all of these sessions end up on different backend
mailservers, and it's basically a crapshoot which Dovecot instance notices a
new message first. NFS locking being what it is, odds are an index will get
corrupted sooner or later, and when this happens the user's mail
'disappears' until Dovecot can reindex it. The users inevitably freak out
and call the helpdesk, who tells them to close and reopen their mail client.
Maybe you're small enough to not run into problems, or maybe your users just
have lower expectations or a higher pain threshold than ours. Either way,
it's unpleasant for everyone involved, and quite easy to solve with the
director proxy.

Timo has been saying for YEARS that you need user-node affinity if you're
doing NFS, and now he's done something about it. If you've already got a
load balancer, then just point the balancer at a pool of directors, and then
point the directors at your existing mailserver pool.

<shameless plug>
For health monitoring on the directors, check out:
http://github.com/brandond/poolmon
</shameless plug>

-Brad