[CentOS] clustered mail server?

Sun May 18 22:25:07 UTC 2008
Christopher Chan <christopher at ias.com.hk>

Karanbir Singh wrote:
> Christopher Chan wrote:
>> No, mail spools/queues do not need replication. Stuff in the queue are 
>> usually deleted in a second and such dynamic change is not worth 
>> replicating. If you do put the queue on a distributed filesystem, in 
>> most cases you cannot have more than one instance running save for 
>> sendmail.
> 
> I think your statement here is flawed, in that if there is even a single 
> bit of the process you dont replicate - you've already lost the HA game.

I am sorry but I do not share that view for incoming mail. The latency 
in getting the mail replicated probably is longer than it takes to do 
the actually delivery to the mail store.

> 
> Besides, as John already pointed out, emails in the spools can hang 
> around for days. I believe most MTA's only discard completely after 
> 7days of non delivery.

That default setting is no longer applicable today. Users will scream if 
they find out that their mails have been sitting in the queue for a day. 
For today's businesses, one day can make or break a deal and so email, 
being a much faster form of communication than snail mail, has come to 
be seen as the preferred choice. People start calling when they know 
they are supposed to get an email in a minute or so when it does 
materialize.

> 
> the OP is taking about DRBD in a primary-> secondary setup, in which 
> case, there wont be a clustered filesystem on the block device, and 
> there will only really be one instance of the real app running.
> 
> 

He is welcome to replicate the queue. His traffic levels will be so low 
that it really does not affect things but if he is using qmail I hope 
that the filesystem is completely identical on the secondary.