High availability of Dovecot

[Gerald Galster]

> Am 11.04.2019 um 13:45 schrieb Patrick Westenberg via dovecot <dovecot at dovecot.org>:
> 
> Gerald Galster via dovecot schrieb:
> 
>> mail1.yourdomain.com <http://mail1.yourdomain.com> IN A 192.168.10.1
>> mail2.yourdomain.com <http://mail2.yourdomain.com> IN A 192.168.20.1
>> 
>> mail.yourdomain.com <http://mail.yourdomain.com>  IN A 192.168.10.1
>> mail.yourdomain.com <http://mail.yourdomain.com>  IN A 192.168.20.1
>> 
>> 
>> mail1/mail2 is for direct connection (MTAs)
>> 
>> Your users (outlook, thunderbird, ...) connect to mail.yourdomain.com
>> <http://mail.yourdomain.com> which returns the two ip addresses.
>> 
>> In this scenario MUA just connects to mail.yourdomain.com
>> <http://mail.yourdomain.com> and randomly uses one of the two ips. You
>> can't control which one, but this gives you active/active loadbalancing.
>> In case one server is down the MUA just uses the other ip.
> 
> Are you sure that this is working?


yes, I'm running a two node dsync cluster in production for a few years without issues.
The system was even working during a whole datacenter outage because the nodes reside
in different, distant locations. I would'nt use a filesystem like ceph with distant
locations due to latency issues. dsync replication is asynchronous, so there is no problem.

Most cluster systems that use drbd, ceph, keepalived, pacemaker, whatever are operated
within a single datacenter or datacenter park. If the datacenter goes down, your
cluster is not reachable anymore. This is a rare event but within 10-15 years it happens
to a lot of datacenters.

Best regards
Gerald