On Tuesday, 2 February 2021 11:37:01 CET Andrea Chierici wrote:
> Hi,
> I am trying to configure high availability on a critical VM. My ovirt
> version is 4.3.10.4-1.el7.
> My question is about the best settings to specify, since it's not
> completely clear to me how they influence the availability.
>
> What I want is simply to have a specific machine ALWAYS running, or at
> least, to be available as much as possible. I have no special
> requirements on the VM, if it goes down, simply restarting it is fine.
>
> Here is my current setting. Is it good or I'd better chage anything?
you may want to configure VM lease. If you don't do so, in case of split
brain, there can be two VMs running and accessing the same storage, leading to
the data corruption. With VM leases this cannot happen - only one VM can
access the storage. To speed up the switch, you may want to configure also
watchdog. But there can be use cases (e.g. stateless server which just
forwards received packet somewhere) where leases are not needed or not using
them won't cause any harm. See [1] for more details.
[1] https://www.ovirt.org/develop/ha-vms.html
Indeed, configuring a VM lease and a watchdog device can be useful.
Not only that a VM lease can generally prevent split brains but in case the host that the VM runs on becomes non-responsive, the system would automatically try to restart the VM elsewhere (otherwise, the system waits for a confirmation from the admin that the host is down which can take time, and yes, if the VM still runs on the non-responsive host can lead to a split-brain).
The watchdog device identifies problems from within the guest that are otherwise hard to identify from outside of the virtual machine. Richard Jones wrote a nice post about the watchdog device few years ago [2]
>
>
> Thanks,
> Andrea
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