[Dovecot] A new director service in v2.0 for NFS installations

[Brad Davidson]

Timo,

> -----Original Message-----
> From: dovecot-bounces+brandond=uoregon.edu at dovecot.org
[mailto:dovecot-
> 
> The company here in Italy didn't really like such idea, so I thought
about
> making it more transparent and simpler to manage. The result is a new
> "director" service, which does basically the same thing, except
without SQL
> database. The idea is that your load balancer can redirect connections
to
> one or more Dovecot proxies, which internally then figure out where
the
> user should go. So the proxies act kind of like a secondary load
balancer
> layer.

This looks very cool! We run a basic two-site active-active
configuration with 6 Dovecot hosts in either location, with an
Active/Standby load balancer cluster in front, and a cluster of
geographically distributed NFS servers in the back. I'm sure I've
described it before. We'd like to keep failover as simple as possible
while also avoiding single points of failure. I have some questions
about the suggested configuration, as well as the current
implementation.

* Does this work for POP3 as well as IMAP?

* Is there any reason not to use all 12 of our servers as proxies as
well as mailbox servers, and let the director communication route
connections to the appropriate endpoint?

* Does putting a host into 'directed proxy' mode prevent it from
servicing local mailbox requests?

* How is initial synchronization handled? If a new host is added, is it
sent a full copy of the user->host mapping database?

* What would you think about using multicast for the notifications
instead of a ring structure? If we did set up all 12 hosts in a ring, it
would be conceivable that a site failure plus failure of a single host
at the surviving site would segment the ring. Multicast would prevent
this, as well as (conceivably) simplifying dynamic resizing of the pool.

Thanks!

-Brad