[Starlingx-discuss] live migration and CPU compatibility

[Kopec, Gerald (Gerry)]

Hi folks,
A couple weeks back, we merged a commit to our nova config in starlingx to default libvirt/cpu_mode option to host-model.
https://review.opendev.org/#/c/669544/

This means that the guest model will closely match the host, see nova docs for more details:
https://docs.openstack.org/nova/latest/admin/configuration/hypervisor-kvm.html#specify-the-cpu-model-of-kvm-guests

However, as part of the live migration prechecks on bare metal environments, nova will compare source and destination hosts for CPU compatibility.  If they are not compatible, then live migration will fail.  Symptoms will be that the instance will not migrate and you'll see an exception in the nova-compute logs with reason: "Unacceptable CPU info: CPU doesn't have compatibility".

Our expectation is that most customers would have homogeneous hardware and if not they would organize their hosts into live migratable groups via the nova host aggregates capability.  Same principle applies to test environments so you may have to update lab configuration and automated tests.

Gerry
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