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

[Thomas Suckow]

I would move the imap.* to a neverland address while doing the switch
so users arn't opening email while files are being rsynced.

OR, just add a firewall rule to old server blocking imap.

I would also send a notice to uses a few days (preferably a week in a
large setup) saying that email may be intermittently unavailable at
9pm on bla bla day while we perform maintenance on our servers to
improve our service to you.

Have a place on your site where they can check the status of the move
and it should avoid "most" phone calls.

Thomas Suckow



On Thu, Aug 13, 2009 at 9:48 PM, Timo Sirainen<tss at iki.fi> 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?
>
>> Is there anything else I should think about to mitigate users noticing
>> a change?
>
> If the maildirs are identical and no mails get lost during the move, that
> should be it.
>
>>  Does the fact that the mail filenames include
>> 'foo.example.org' in the file name (while new deliveries to
>> bar.example.org will include that new hostname) spell trouble later on
>> or can I ignore it?
>
> Filenames don't matter.
>
>> And finally, dovecot on foo.example.org is 1.1.7 while the new server
>> is running 1.1.16.  I don't think that should be an issue, but
>> mentioning it just in case.
>
> Whenever upgrading it's a good idea to go through the items marked with "*"
> in NEWS file (http://dovecot.org/doc/NEWS-1.1) There aren't many usually.
>