On Thu, May 24, 2018 at 2:20 PM wodel youchi <wodel.youchi@gmail.com> wrote:

Hi,

Excuse the English :)

Need some advice regarding the use of high availability software on VMs on oVirt.

We are migrating a physical high available application to oVirt.
The HA platform uses pacemaker, it contains two nodes and a shared storage, fence (stonith) is configured to use ILO.

I know that oVirt offers HA for VM, but this HA is not application aware, if a service crashes on the VM, it will not be detected.
Fencing could be achieved by fence agent rhev.

My questions are about the best way to migrate this platform to oVirt.

- Is it a good idea to make both VMs (formally nodes) Highly-Available VMs? or may be pin each one of them to a particular hypervisor and/or use VM-Affinity?

If the VM should be highly available, you should not pin them to any host.

Pinning them will make sure the vm will *not* be available when the host

is down :-)

So you probably want to use HA VM - with a VM lease.

Warning: do not use HA VM without a VM lease, this will make sure that

you will have split-brain eventually.

- I am thinking about the situation where the hypervisor containing one of the VMs crashes, what will be the behavior of the the fence agent on the application?

Not sure what do you mean by "crashes".

If the hypervisor lost power, HA VM with a VM lease will be started on another

hypevisor.

The guest agent on the VM will not be able to do anything since it is not running :-)

- if the crashed VM is not HA, it will not start on another hypervisor, so the fence agent will try to fence a VM that does not exist anymore, and it will stuck.
- if the crashed VM is HA, it will be started on another hypervisor, but what will happen with the fence agent? I think that one VM will fence the other one, and the application will still be unreachable for a longer period.

Not clear what fence agent are you talking about.

- What about the shared storage, we will use a shared disk on oVirt which does not support snapshot

What is the question?

- What are the things to avoid?

I think in general, don't try to have two mechanisms that try to do the same.

Either use your HA solution or oVirt HA solution, but not both in the same time.

Nir