Multiple servers and NFS

[Eduardo Ramos]

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