dovecot - Jul 2014 - Multiple servers and NFS

Hi all,

For some reason, I didn't go to http://wiki2.dovecot.org/NFS until now, 
and I'm starting to get worried ...

The plan was to have multple servers (MXes) receiving mail, and 
delivering via LMTP to multiple backend dovecot servers (with amavis in 
front of dovecot; LMTP both sides). Then we'd have multiple servers for 
clients to use IMAP or POP3.

This is more or less how the system already works, except with Courier 
IMAP, and postfix on the backends, delivering to maildirs with procmail.

But with the recommendation to use the Director for both IMAP/POP3 and 
LMTP - that starts to sound like I need a whole bunch more servers to 
run Directors and proxies, and even then it might not be a good idea to 
have different servers running lmtp and imap/pop.

One possible mitigating point is that our 'load balancing' is DNS 
round-robin, so a given client will probably stick with a single 
imap/pop server anyway, but if the user has multiple clients 
(desktop/mobile etc) then they may still hit different servers.

Can someone clarify best practice for a setup needing multiple servers 
for load balancing and redundancy?

Is Courier already likely to have been suffering these problems?

Oh, the NFS server is a NetApp Filer, if that matters.

I'm using dovecot 2.2.9 from debian wheezy backports, in order to get 
the quota policy daemon support.

Thanks,
Richard

Richard Hector wrote:
> But with the recommendation to use the Director for both IMAP/POP3 and LMTP
> - that starts to sound like I need a whole bunch more servers to run
> Directors and proxies, and even then it might not be a good idea to have
> different servers running lmtp and imap/pop.
Running Multiple Invocations of Dovecot is totally sufficient:

http://wiki2.dovecot.org/RunningDovecot
http://wiki2.dovecot.org/Tools/Doveadm/Instance

Regards
Daniel

Hi Richard,

You can use one or more instances of Dovecot on the same machine, as you 
can see here (http://wiki2.dovecot.org/RunningDovecot) "Running Multiple 
Invocations of Dovecot".

The problem with DNS round-robind is that if you server goes down, DNS 
continues resolving for it. I would recommend use some balancer like 
LVS+keepalived.

Consider that multi layer solution:
--------------------            --------------------
| LVS + keepalived |            | LVS + keepalived |
--------------------            --------------------
          |                                |
   --------------                   --------------
   | Director 1 |                   | Director 2 |
   --------------                   --------------
          |                                |
  -----------------               -----------------
  | IMAP/POP/LMTP |               | IMAP/POP/LMTP |
  |    Backend    |               |    Backend    |
  -----------------               -----------------
          \                                /
           \                              /
            \       ------------         /
             -------|  NetAPP  |---------
                    ------------

Remember, directors and backends could run on the same machine. I have a 
lab running that way. Maybe I can help you deploy.
On 07/23/2014 07:23 PM, Richard Hector wrote:
> Hi all,
>
> For some reason, I didn't go to http://wiki2.dovecot.org/NFS until 
> now, and I'm starting to get worried ...
>
> The plan was to have multple servers (MXes) receiving mail, and 
> delivering via LMTP to multiple backend dovecot servers (with amavis 
> in front of dovecot; LMTP both sides). Then we'd have multiple servers 
> for clients to use IMAP or POP3.
>
> This is more or less how the system already works, except with Courier 
> IMAP, and postfix on the backends, delivering to maildirs with procmail.
>
> But with the recommendation to use the Director for both IMAP/POP3 and 
> LMTP - that starts to sound like I need a whole bunch more servers to 
> run Directors and proxies, and even then it might not be a good idea 
> to have different servers running lmtp and imap/pop.
>
> One possible mitigating point is that our 'load balancing' is DNS 
> round-robin, so a given client will probably stick with a single 
> imap/pop server anyway, but if the user has multiple clients 
> (desktop/mobile etc) then they may still hit different servers.
>
> Can someone clarify best practice for a setup needing multiple servers 
> for load balancing and redundancy?
>
> Is Courier already likely to have been suffering these problems?
>
> Oh, the NFS server is a NetApp Filer, if that matters.
>
> I'm using dovecot 2.2.9 from debian wheezy backports, in order to get 
> the quota policy daemon support.
>
> Thanks,
> Richard