[Dovecot] HA Dovecot Config?

[Eric Rostetter]

Quoting dovecot at corwyn.net:

> As I look at upgrading the mail server, I'd like to change to a  
> higher availability configuration (where the server can fail and I  
> don't have to reconfig my imap users).

Sounds like a great plan!

> For the SMTP that's easy, because I can use multiple MX records, and  
> I can redirect a port forward from one server to another. But IMAP  
> doesn't have the same functionality, because it's the storage that  
> matters.

True for SMTP as long as you handle the SSL certificate issue, or don't
use encryption.

For IMAP to be truely HA, you will need shared storage of some sort.

> What's the "best" way to do that?  Clustered servers using a SAN?  
> NAS? some sort of appliance in front?  Suggestions?

There is no single "best way" since it will depend on your budget, skills,
etc.

Certainly a SAN is one way to go, and allows for possibly active-active
setups (depending on file system) and great flexibility.

You could also try that with NAS if you are careful enough.  SAN
is more complex to setup than a NAS, but NAS is harder to setup correctly
for dovecot than a SAN would be, so flip a coin there.

You can "emulate" a SAN with something like DRBD if budget doesn't allow a
real SAN (that is what I do).

Or you could do multi-attached active-passive disk systems (external disk
tray is physically connected to 2 machines in active-passive setup).

Which to use depends on knowledge/skill, costs/budget, type of
cluster/failover needed, vendor support if that matters to you, etc.

I setup mine as a pair of redundant front-end firewalls (linux heartbeat)
which connect to a trio of Red Hat Cluster Suite machines using DRBD+GFS
(two nodes do DRBD+GFS and handle SMTP+POP3+IMAP4, while the third node
does _NOT_ do DRBD+GFS, and simply does the webmail interface).

> Thanks!
>
> Rick

-- 
Eric Rostetter
The Department of Physics
The University of Texas at Austin

Go Longhorns!