[Herefordshire] High Availability Linux

[john at drystone.co.uk]

On Fri, Jan 28, 2005 at 08:35:06AM -0000, Chris Bond wrote:
> Hi,
> 
> Just wondering if anybody here has any experience with High Availability
> Linux?  I've just received three new servers to migrate my current exim
> setup too, I want to do it using high availability so there's no downtime
> though.
> 
> So far I've got the following:
> - Redhat 3.0 Enterprise
> - Redhat do there own clustering software however, im not sure if its what I
> want
> - /var/dspam and /home/mail need to be fully sych' incase of fallover, I
> could either do this using external scsi enclosure or using something like
> drbd.org
> - Mysql 4 - full replication to secondary box
> - Full service fallover, for bind, apache, exim, pop3, imap - the linux HA
> project with a heartbeat should be able todo this.
> - Want to advertise at least 2 hosts minimum in DNS so there's always a
> route for mail
> 
> - Im currently using gradwell.net service for backup mail, however, the
> third box I would like to put that at our office not the datacenter,
> therefore being able to run secondary dns, backup mx, full replication
> (prolly rsych) of data from main boxes as certain periods.
> 
> Any pointers as its quite a complex setup im trying to archive!  Should be
> fun setting it up though.  Im in no rush to replace the current mail servers
> as there currently coping very well, this is purely being put in for furture
> expansion and resilent.
> 
> Kind Regards,
> Chris Bond

Hi Chris

I confess to having no experience with clusters but, conincidentally,
yesterday I read an article in next months (Feb 05) PCPlus about using
heartbeat for failover. I'll can email it to you if you like. It sounds
as though you are on the right track with heartbeat, drdb, rsync etc.

For mail, a single DNS entry should suffice as your failover will have
the same IP. Secondary MX is a little redundant as most mail servers
will keep resending for a few days at least and your HA cluster will
allways be, well, available :) Spammers sometimes exploit secondary MX
in the hope that there will be less spam checking etc on backup hosts,
so maybe use it only if you can keep the mailserver configs in sync.

This all sounds great fun! It would be good to hear of your experiences
when the cluster is up and running. It will be really handy to be able
to switch off a box for maintenance without interrupting services.

Cheers

John