[Dovecot] Load Balancing and HA

[Andreas Kasenides]

On 31-05-2013 12:57, Patrick Westenberg wrote:
> Romer Ventura schrieb:
>
>> 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
>
> Your proxy won't reconnect a user to backend B if the backend A 
> fails.


But doesn't that depend on how the vitual IP is managed ie what kind of 
system is behind it?
For example a simple heartbeat setup would correct this at the cost of 
one machine sitting idle.
Other setups using load balancers can correct this.

There is a better solution using the Director service of Dovecot where 
users are assigned
to one of several bacend machines and disconnected when idle. Even, 
there is a script that monitors the health
of the Director backends and adjusts accordingly (which I haven't 
personally tried yet). See
http://wiki2.dovecot.org/Director
http://www.dovecot.org/list/dovecot/2010-August/051946.html