Wed Jun 22 06:10:24 UTC 2016
Tom Robinson <tom.robinson at motec.com.au>

Hi Digimer,

Thanks for your reply.

On 22/06/16 15:20, Digimer wrote:
> On 22/06/16 01:01 AM, Tom Robinson wrote:
>> Hi,
>> I have two KVM hosts (CentOS 7) and would like them to operate as High Availability servers,
>> automatically migrating guests when one of the hosts goes down.
>> My question is: Is this even possible? All the documentation for HA that I've found appears to not
>> do this. Am I missing something?
> Very possible. It's all I've done for years now.
> https://alteeve.ca/w/AN!Cluster_Tutorial_2
> That's for EL 6, but the basic concepts port perfectly. In EL7, just
> change out cman + rgmanager for pacemaker. The commands change, but the
> concepts don't. Also, we use DRBD but you can conceptually swap that for
> "SAN" and the logic is the same (though I would argue that a SAN is less
> reliable).

In what way is the SAN method less reliable? Am I going to get into a world of trouble going that way?

> There is an active mailing list for HA clustering, too:
> http://clusterlabs.org/mailman/listinfo/users
I've had a brief look at the web-site. Lots of good info there. Thanks!

>> My configuration so fare includes:
>>  * SAN Storage Volumes for raw device mappings for guest vms (single volume per guest).
>>  * multipathing of iSCSI and Infiniband paths to raw devices
>>  * live migration of guests works
>>  * a cluster configuration (pcs, corosync, pacemaker)
>> Currently when I migrate a guest, I can all too easily start it up on both hosts! There must be some
>> way to fence these off but I'm just not sure how to do this.
> Fencing, exactly.
> What we do is create a small /shared/definitions (on gfs2) to host the
> VM XML definitions and then undefine the VMs from the nodes. This makes
> the servers disappear on non-cluster aware tools, like
> virsh/virt-manager. Pacemaker can still start the servers just fine and
> pacemaker, with fencing, makes sure that the server is only ever running
> on one node at a time.

That sounds simple enough :-P. Although, I wanted to be able to easily open VM Consoles which I do
currently through virt-manager. I also use virsh for all kinds of ad-hoc management. Is there an
easy way to still have my cake and eat it? We also have a number of Windows VM's. Remote desktop is
great but sometimes you just have to have a console.

> We also have an active freenode IRC channel; #clusterlabs. Stop on by
> and say hello. :)

Will do. I have a bit of reading now to catch up but I'm sure I'll have a few more questions before

Kind regards,

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