[Dovecot] Gotchas in switching from one server to another without impacting users?

[Sahil Tandon]

On Fri, 14 Aug 2009, Timo Sirainen wrote:

> On Aug 14, 2009, at 12:36 AM, Gary Chodos wrote:
>
>> We have to replace one mail store (foo.example.org) with another
>> (bar.example.org).  I rsync'd the maildirs from foo to bar today and
>> the plan is to hold all delivery (in the SMTP server) on foo over the
>> weekend, rsync again (this time it should be much faster since the
>> large xfer already occurred today), then flush the SMTP queue on foo
>> towards bar, direct all new deliveries to bar.example.org.  Users
>> currently access their IMAP mailboxes via imap.example.org.  I plan to
>> just 'flip the switch' at DNS so imap.example.org points to
>> bar.example.org (instead of foo.example.org) so users don't have to
>> change anything on their end and should not even notice this change.
>
> And I guess you also thought about the DNS cache TTLs?

The OP should also consider killing dovecot during the rsync (similar to what
another member of this list suggested).  Then restart with a new
configuration that proxies incoming IMAP connections towards the new server
in case some clients still hit the old server before full DNS propagation.

-- 
Sahil Tandon <sahil at tandon.net>