[nSLUG] XEN & Heartbeat

Oliver Baltzer oliver at hytek.org
Tue Jun 2 22:35:25 ADT 2009


Hi Miles,

I do not have experience with a particular setup like this, but if you
do not have access to a multi-path SAN I would use DRBD to simply mirror
the SATA devices on both physical machines including the configurations
of the VM and then only start the VMs you want on each of the systems.
Then, if one of the physical machines goes away, you can automatically
start the lost VM on the remaining physical system. Of course that would
be like booting from a cold shutdown. You would loose any open sockets
and data that was not flushed on the lost machine as well as any DRBD
data that was in transit. However, any stand-by based HA solution would
have these problems and the damage is typically within acceptable limits.

If you actually know in advance that one of your physical machines will
go away, you can migrate the running VM from one system to the another
online. I have never done this with Xen, but you might even be able to
take the open sockets with you, then the transition would be completely
transparent to any clients.

I hope this helps.

Cheers,
Oliver

Miles Thompson wrote:
> We're looking at replacing our web and email servers; hypervisor's intrigue me.
> 
> If anyone has experience with this, would it be possible to have two 
> boxes, call them Left and Right. Both running XEN and configured with 
> identical virtual machines, with this software:
>   - Apache
>   - MySQL
>   - Pure-ftp
>   - iFolder
>   - Postfix / CYRUS
> 
> Email and iFolder would each get their own virtual machines.
> 
> Heres the crunch, I think. Could the load be split this way:
> Left:
> - web server
>    (3 sites and 3 IPs, as each has its own SSL cert)
> - FTP (another IP and SSL cert)
> - iFolder
> 
> Right:
> - email server
> 
> Disk configuration: MIrrored terabyte SATA disks in each box, and 
> heartbeat keeps them in sync.
> 
> (Remember - the two boxes are configured identically, I really just 
> want to split the load. Our email server is much busier than the web servers.)
> 
> Thoughts? Suggestions?
> 
> Regards - Miles
> 
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