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:
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 long.
Kind regards, Tom