dovecot - Nov 2018 - Multi-server but small scale

I have a small but critical server that supports our group.? As a single 
server - it's obviously a single-point-of-failure for lots of things.? 
As I just experienced...again.? It was a lot more fun building systems 
from components when I was younger...

Previously 3rd-party hosted solutions didn't look attractive for several 
reasons...but I'm seeing prices now for cloud virtual machines that are 
stupid cheap.? Even if they wind up being limited speed & availability - 
it would seem they'd be a lot better than nothing!

So I'm considering having at least one backup server for various 
services - obviously that includes mail.? So now I have to wonder about 
the backend.? And while I think I'm reasonably current with networked 
file systems (not distributed or cluster) I haven't played with 
replication for a quite a while.

For this particular usage (I'm envisioning two servers total) - is there 
a need/reason to use any form of networked/distributed/cluster file 
storage?? Or would this be accomplished via "pure" Dovecot - dsync 
replication would keep things updated between the servers and director 
would handle the connections?? So with identically configured SMTP 
servers, passing to the local LMTP agents, the file system would be 
"purely local" with no NFS or other interconnection?

-- 
Daniel

Hi,

if you have only one pair of servers, I think replication via dovecot's
dsync (or doveadm via ssh) where each server holds all emails as a
local storage would be easiest.?

There is a caveat with shared folders though. And dovecot replicates
only emails. The index is not included, which means for example that
you'd need 2 databases for quota - otherwise emails would count twice.
Well and any manual index management needs to be done on both sides.

https://wiki.dovecot.org/Replication

Running a cluster filesystem or NFS as a common base is possible but
needs some adjustments of dovecot like turning off caching or memory
mapping, which in turn decrease performance.

This is only some short handbook knowledge as I haven't implemented
replication yet.

Greetings
Martin Johannes Dauser

On Mon, 2018-11-19 at 17:51 -0800, Daniel Miller wrote:
> I have a small but critical server that supports our group.? As a
> single?
> server - it's obviously a single-point-of-failure for lots of
> things.??
> As I just experienced...again.? It was a lot more fun building
> systems?
> from components when I was younger...
> 
> Previously 3rd-party hosted solutions didn't look attractive for
> several?
> reasons...but I'm seeing prices now for cloud virtual machines that
> are?
> stupid cheap.? Even if they wind up being limited speed &
> availability -?
> it would seem they'd be a lot better than nothing!
> 
> So I'm considering having at least one backup server for various?
> services - obviously that includes mail.? So now I have to wonder
> about?
> the backend.? And while I think I'm reasonably current with
> networked?
> file systems (not distributed or cluster) I haven't played with?
> replication for a quite a while.
> 
> For this particular usage (I'm envisioning two servers total) - is
> there?
> a need/reason to use any form of networked/distributed/cluster file?
> storage?? Or would this be accomplished via "pure" Dovecot -
dsync?
> replication would keep things updated between the servers and
> director?
> would handle the connections?? So with identically configured SMTP?
> servers, passing to the local LMTP agents, the file system would be?
> "purely local" with no NFS or other interconnection?
>