[Dovecot] High Availability strategies

[Robert Schetterer]

Joseba Torre schrieb:
> Hi,
> 
> we have a medium setup (8000 pop and imap users using almost every 
> available client, 800GB of stored mails using maildir on a Celerra NFS 
> server, with index files on local disks, and procmail for local 
> delivery), being served by a Dell PowerEdge 2850 (2GB RAM and dual P4 
> Xeon 3,2GHz).
> 
> Our current not-so-high availability setup is based on a similar 
> server with the same setup and a easy but manual process to switch 
> from one server to another.
> 
> We are thinking about  setting up some kind of serious high 
> availability, but for every strategy we think about some problems 
> appear, and I'd like to hear your opinions about them:
> 
> - The recommended setup, with each user being sent always to the same 
> server, is not possible because our load balancers (Cisco Catalyst 
> 6000) can't do that.
> 
> - We could put both servers behind the load balancer, and keep local 
> index files on each server. Usually the same ip we'll be redirected to 
> the same server, so few problems will arise. When a user is sent to a 
> new server, index will be rebuilt so performance will be bad but we 
> should not expect other problems, right?
> 
> - We could also put the index files on a nfs share. No problems, but 
> pretty bad performance.
> 
> - We could also get more ram for the servers and keep indices in 
> memory.
> 
> How can we compare these solutions? Apart from performance, are other 
> problems expected? Using deliver instead of procmail could improve 
> performance?
> 
> - We've also thought about some more or less weird setups, like 
> setting up a GFS filesystem for the index files, or setting up a proxy 
> on every server which redirect users to their fixed server, but they 
> seem too complex for few advantages.
> 
> Any recommendations? How are you doing this? 

search the list archive, this  was disscussed before
a ha balance setup with gfs like filesystem is possible and
working, sorry about cisco i only did small tests
plain ha linux setups with a layout of 4 servers
2 ha loadbalancers and 2 postfix/dovecot servers
on ubuntu with one cluster ip, but posibilities
are serveral ways to goal what you need, so fitting to local network
layouts is always needed as well as hard testing before production stage

is always needed
-- 
Best Regards

MfG Robert Schetterer

Germany/Munich/Bavaria