Feature Request - Director Balance

[Webert de Souza Lima]

Shrinking director_user_expire might be a workaround but not as good as a
solution, as also the user can end up mapped to the same server again.
Director flush is both manual and aggressive, so not a good solution too.

The possibility to move users between backends without killing existing
connections is a good solution, yes! It can be scripted. =]

What I suggested was more automated, but that can be left for a future
future. If you have a command to be manually issued like:  "doveadm
director rebalance" it would be great.

Thanks for your feedback.

Att,

Webert de Souza Lima
MAV Tecnologia.


On Fri, Apr 21, 2017 at 4:52 AM, Timo Sirainen <tss at iki.fi> wrote:

> On 20 Apr 2017, at 17.35, Webert de Souza Lima <webert.boss at gmail.com>
> wrote:
> >
> > Hi,
> >
> > often I run into the situation where a dovecot server goes down for
> > maintenance, and all users get concentrated in the remaining dovecot
> server
> > (considering I have 2 dovecot servers only).
> >
> > When that dovecot server comes back online, director server will send new
> > users to it, but the dovecot server that was up all the time will still
> > have tons of clients mapped to it.
> >
> > I suggest the director servers to always try to balance load between
> > servers, in the way:
> >
> > - if a server has several more connections than other, mark it to
> > re-balance
> > - when a user connected to this loaded server disconnects, map it to
> > another server (that is per definition not the same server) immediately.
> >
> > that way it would gracefully re-balance, not killing existing
> connections,
> > just waiting for them to finish.
>
> You could effectively do this by shrinking the director_user_expire time.
> But if it's too low, it causes director to be a bit more inefficient when
> assigning users to backends. Also if backends are doing any background work
> (e.g. full text search indexing) director might move the user away too
> early. But setting it to e.g. 5 minutes would likely help a lot.
>
> There's of course also the doveadm director flush, which can be used to
> move users between backends, but that requires killing the connections for
> now. I've some future plans to make it possible to move connections between
> backends without disconnecting the IMAP client.
>