[CentOS] clustered mail server?

Sun May 18 05:24:53 UTC 2008
Rudi Ahlers <Rudi at SoftDux.com>

John R Pierce wrote:
> Rudi Ahlers wrote:
>> Sorry guys, I want to stick with a SMTP / IMAP / POP3 server, not 
>> webmail. I'll be using Horde for webmail as well though
> there are two general classes of clustered systems, high availability, 
> and high performance.
> HA clusters are usually active/standby, and might use stuff like 
> heartbeat, drbd, etc.
> HP clusters are either load balanced, or active/active...  Things that 
> demand ACID (Atomicity, Consistency, Isolation, Durability) like 
> databases, mail servers are very complex to cluster this way on a 
> active/active (aka multimaster) environment while maintaining the 
> integrity and a reasonable performance.  just implementing load 
> balancing does not by itself provide any redundancy in case of 
> component failure.   A simple load balancing scenario for a mail 
> server might be having one server to handle all internet mail incoming 
> and outgoing, while another server handles local users reading their 
> mail (eg, pop or imap)
> its best to define your requirements and expectations before diving 
> into these waters, as clusters can be far more complex and intricate 
> to configure and administrate than discrete systems.
> re: mail servers specifically, there are two seperate classes of 
> storage that would need replication...  One is the mail spools and 
> queues as used by the MTA (postfix, sendmail, etc), and the other are 
> the user mail folder(s) as used by the local delivery agent (procmail 
> or whattever), and read by the mail client (pop, imap).
> _______________________________________________
Ok, I see where you're going, and a bit of clarification is needed :)

I need a simple failover type cluster, where any 1 of the 2 machines 
currently in the "cluster" can handle anything. The client (a small 
rural clinic) is 700KM's away, and they do have frequent power failures, 
so bad that even the UPS' lifespan has shorten. This is a donated 
project, so funds (and hence equipment / reliable equipment) is limited. 
We currently have 2servers with Dual Core PIV + 2GB RAM + 2x 160GB HDD's 
each. The HDD's is setup on RAID1, and the two servers replicate MySQL 
on an active/active (Master - Master) replication. The intranet site & 
file server data is being replicated via rsync. This all works well, but 
I need a mail server.

The main server will store all the emails (like an exchange server 
does), the users will use IMAP (so, a) it's backed up & b) they can 
always access their email from any workstation) & SMTP, with the ability 
to use POP3 from home / on the road. It would be nice to have a shared 
calendar & address book as well, so something like phpgroupware / open 
exchange / etc would be nice.

But, I don't need load balancing, just high availability


Kind Regards
Rudi Ahlers
CEO, SoftDux

Web:   http://www.SoftDux.com
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