[Dovecot] Load Balancing and HA

[Andreas Kasenides]

I am actually going through the first stages of implementing your 
Scenario1.
There is small difference: there will also be 2*Postfix relays also on 
the
Dovecot Proxies. This allows placing them in a DMZ such that the "real"
Dovecot/Postfix servers are placed away from the WAN.

After much arguing and thinking I decided to go with this option
as the most basic and possibly the simplest way to achieve MY goals:
1. fault tolerance of the entire system such that a failure will not
impact mail delivery/access.
2. distribute users on at least two Dovecot servers to help when peak 
times arrive.
3. Ability to expand easily if demand rises
4. No use of custom hardware
5. Both internal (LAN) users and "away from office" (WAN) users will 
"see"
the same setup to ease configuration (mostly done by users these days)

I should say that other more complicated setups like full blown 
clusters and
distributed file systems have been rejected due to their complexity 
(and the
fact we do not have experience with them).
Our user base is around 3-4K of heavy users.

Andreas


On 29-05-2013 00:23, Romer Ventura wrote:
> Hello,
>
>
>
> I've been thinking about the best way to achieve load balancing and 
> making
> my mail servers highly available. So far I believe I have 2 
> scenarios:
>
> Scenario1: This should allow any to lose any of the servers and 
> clients
> still have access to their emails (although I am not sure how the 
> indexes
> would react to this and sudden disconnection)
>
> -          2 Dovecot Proxy servers, using a virtual IP to where the 
> clients
> will connect to from the WAN and LAN
>
> -          2 Dovecot+Postfix servers with local cache
>
> -          2 NFS servers and synced with dsync (mirror, 1 server 
> writes to
> its own NFS and changes synced to the other via dsync)
>
>
>
> Scenario2: Pretty much as above on the back end. However, with this 
> there is
> no way to load balance users.
>
> -          2 Dovecot+Postfix server with local cache
>
> -          2 NFS servers synced with dsync
>
> -          Make use of DNS MX record priority to provide access to 
> secondary
> email server
>
>
>
>
>
> Anyone care to comment?
>
>
>
> Thanks.