[Linux-cluster] RH Cluster Suit can be used to create a qmail cluster?

[Rainer Duffner]

Am 19.06.2007 um 23:19 schrieb Roger Peña:

> Hi
>
> I am looking for ideas about to create a Qmail HA
> cluster with 2 nodes and the storage in a SAN (FC
> access)
>


Only two nodes?
What backend do you want to use?
(In case you want to use vpopmail)


> right now I am in the design stage, mainly finding
> potencial problems so ....
> do anybody has anything to recommend ?


Qmail is IMO not suited for a GFS cluster.
GFS tries its best to keep write operations on the cluster-FS  
synchronized.
This is useless in the case of Qmail, because Qmail is designed to  
function even on NFS-filesystems without any kind of useful locking.
In GFS-land, Qmail just generates lots of useless I/O.


> (except not use qmail ;-) I would like to use postfix
> or exim but my client disagree :-( no choice here)
>


It's understandable. Qmail still offers a lot of value when it comes  
to virtual email-domain hosting - though the original DJB-Qmail is  
barely usable today.
But people like Matt Simerson and Bill Shupp have done tremendous  
integration-work, and helped to keep the platform on par (or in some  
cases beyond) with other systems, even commercial ones.


> my first problem looks like qmail is started,
> monitored and managed by daemontools (sv* programs)
> and svscan itseft is started through inittab or
> rc.local
> so my first approach is to create an sysV init script
> for svscanboot (whitch is used to start svc and
> svscan) and that script is the one that will be
> controlled by RHCS as a script resource (alonside with
> the GFS or plain FS resource, and maybe the IP
> resource)
>


Sometimes, it's not enough to stop the svscan-startscript.
Daemons linger around, prevent new ones from starting. After killing  
the start-scripts, it might be necessary to kill (or kill -9) any  
remaining processes.


> so, my idea is to "clusterizate" (that word exist ?
> ;-) ) the daemontool and not the qmail process, do you
> agree?
>
> thanks in advance for any tip :-)
>


You could try to run a sharedroot-cluster on RHEL4 and see how it  
performs for your workload - there are some succesful reports here on  
this list (though the one I remember uses a tremendous amount of disk- 
spindles).
This should solve your problems with the script (just fence the whole  
node - finished).

If you don't want to go that route, I'd say forget about GFS and go  
back to NFS (with a serious NFS server-platform like Solaris and  
clients like Solaris or FreeBSD) - see the picture on Bill Shupp's  
homepage for a design.
Matt Simerson's formerly FreeBSD-only (now also Solaris, Linux,  
Darwin) Mail-Toaster framework already contains most of the  
integration-work necessary (distribute configfiles etc. - take a look  
at the source, it's amazing).

Above a certain amount of users (500k, probably varies), shared- 
storage may be the wrong answer anyway.
Then, a distributed setup might be better suited.
How many users will you have to support?


cheers,
Rainer
-- 
Rainer Duffner
CISSP, LPI, MCSE
rainer at ultra-secure.de