[Dovecot] Director questions

[Timo Sirainen]

On 23.1.2012, at 21.13, Mark Moseley wrote:

> In playing with dovecot director, a couple of things came up, one
> related to the other:
> 
> 1) Is there an effective maximum of directors that shouldn't be
> exceeded? That is, even if technically possible, that I shouldn't go
> over?

There's no definite number, but each director adds some extra traffic to network and sometimes extra latency to lookups. So you should have only as many as you need.

> Since we're 100% NFS, we've scaled servers horizontally quite a
> bit. At this point, we've got servers operating as MTAs, servers doing
> IMAP/POP directly, and servers separately doing IMAP/POP as webmail
> backends. Works just dandy for our existing setup. But to director-ize
> all of them, I'm looking at a director ring of maybe 75-85 servers,
> which is a bit unnerving, since I don't know if the ring will be able
> to keep up. Is there a scale where it'll bog down?

That's definitely too many directors. So far the largest installation I know of has 4 directors. Another one will maybe have 6-10 to handle 2Gbps traffic.

> 2) If it is too big, is there any way, that I might be missing, to use
> remote directors? It looks as if directors have to live locally on the
> same box as the proxy. For my MTAs, where they're not customer-facing,
> I'm much less worried about the latency it'd introduce. Likewise with
> my webmail servers, the extra latency would probably be trivial
> compared to the rest of the request--but then again, might not. But
> for direct IMAP, the latency likely be more noticeable. So ideally I'd
> be able to make my IMAP servers (well, the frontside of the proxy,
> that is) be the director pool, while leaving my MTAs to talk to the
> director remotely, and possibly my webmail servers remote too. Is that
> a remote possibility?

I guess that could be a possibility, but .. Why do you need so many proxies at all? Couldn't all of your traffic go through just a few dedicated proxy/director servers?