Add a workaround to skip hypervisor version check on live migration

[Kashyap Chamarthy]

What?
-----

Add a workaround config option (that will be disabled by default) that will disable the version-checking of hypervisors during live-migration.

Why?
----

It can be useful for operators in certain scenarios when upgrading. E.g. if you want to relocate all instances off a compute node due to an emergency hardware issue, and you only have another old compute node ready at the time.

Note, though: libvirt will do its own internal compatibility checks, and might still reject live migration if the destination is incompatible.

[sean mooney (sean-k-mooney)]

This is really just a nice to have option for operators that find them selves in an unfortunate situation where they need to move vms to an old hypervisor e.g. rolling back an upgrade or unexpected hardware failure in the middle of an rolling upgrade.

it is not a bug in nova itself nor is it really a feature since it not something we would ever enable by default.

so triaging this as wishlist since its nice to have but not strictly required.
you can use cold migration in this case and if the VM is using a feature form the new hypervisor release that will still be required.

as noted libvirt will do its own internal check and if the VM is using a feature not supported by the dest host it will still reject the live migration. so this is safe but suboptimal since this would make the failure much later in this case.

for operator that are manually intervening and know that the VM will work on the dest the scheduling pessimisation is not a concern and since livemigation is an admin only operation i think this is oke as a workaround.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/yoga
Review: https://review.opendev.org/c/openstack/nova/+/851202

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/xena
Review: https://review.opendev.org/c/openstack/nova/+/851205

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/wallaby
Review: https://review.opendev.org/c/openstack/nova/+/851206

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/victoria
Review: https://review.opendev.org/c/openstack/nova/+/851223

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/ussuri
Review: https://review.opendev.org/c/openstack/nova/+/851224

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/train
Review: https://review.opendev.org/c/openstack/nova/+/851226

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/nova/+/851034
Committed: https://opendev.org/openstack/nova/commit/00ed8a232bc22f48011e95a0b47750520a5b4d47
Submitter: "Zuul (22348)"
Branch: master

commit 00ed8a232bc22f48011e95a0b47750520a5b4d47
Author: Kashyap Chamarthy <email address hidden>
Date: Tue Jul 26 16:02:17 2022 +0200

    Add a workaround to skip hypervisor version check on LM

    When turned on, this will disable the version-checking of hypervisors
    during live-migration. This can be useful for operators in certain
    scenarios when upgrading. E.g. if you want to relocate all instances
    off a compute node due to an emergency hardware issue, and you only have
    another old compute node ready at the time.

    Note, though: libvirt will do its own internal compatibility checks, and
    might still reject live migration if the destination is incompatible.

    Closes-Bug: #1982853

    Change-Id: Iec387dcbc49ddb91ebf5cfd188224eaf6021c0e1
    Signed-off-by: Kashyap Chamarthy <email address hidden>

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 26.0.0.0rc1 release candidate.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/nova/+/851202
Committed: https://opendev.org/openstack/nova/commit/c07495d9d64dd0635d72fc7ff67d73a656a40d13
Submitter: "Zuul (22348)"
Branch: stable/yoga

commit c07495d9d64dd0635d72fc7ff67d73a656a40d13
Author: Kashyap Chamarthy <email address hidden>
Date: Tue Jul 26 16:02:17 2022 +0200

    Add a workaround to skip hypervisor version check on LM

    When turned on, this will disable the version-checking of hypervisors
    during live-migration. This can be useful for operators in certain
    scenarios when upgrading. E.g. if you want to relocate all instances
    off a compute node due to an emergency hardware issue, and you only have
    another old compute node ready at the time.

    Note, though: libvirt will do its own internal compatibility checks, and
    might still reject live migration if the destination is incompatible.

    Closes-Bug: #1982853

    Change-Id: Iec387dcbc49ddb91ebf5cfd188224eaf6021c0e1
    Signed-off-by: Kashyap Chamarthy <email address hidden>
    (cherry picked from commit 00ed8a232bc22f48011e95a0b47750520a5b4d47)

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 25.1.1 release.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Elod Illes <email address hidden>" on branch: stable/train
Review: https://review.opendev.org/c/openstack/nova/+/851226
Reason: stable/train branch of nova projects' have been tagged as End of Life. All open patches have to be abandoned in order to be able to delete the branch.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Elod Illes <email address hidden>" on branch: stable/ussuri
Review: https://review.opendev.org/c/openstack/nova/+/851224
Reason: stable/ussuri branch of openstack/nova transitioned to End of Life and is about to be deleted. To be able to do that, all open patches need to be abandoned.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Elod Illes <email address hidden>" on branch: stable/victoria
Review: https://review.opendev.org/c/openstack/nova/+/851223
Reason: stable/victoria branch of openstack/nova is about to be deleted. To be able to do that, all open patches need to be abandoned. Please cherry pick the patch to unmaintained/victoria if you want to further work on this patch.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Elod Illes <email address hidden>" on branch: stable/wallaby
Review: https://review.opendev.org/c/openstack/nova/+/851206
Reason: stable/wallaby branch of openstack/nova is about to be deleted. To be able to do that, all open patches need to be abandoned. Please cherry pick the patch to unmaintained/wallaby if you want to further work on this patch.

[OpenStack Infra (hudson-openstack)]

Change abandoned by "Elod Illes <email address hidden>" on branch: stable/xena
Review: https://review.opendev.org/c/openstack/nova/+/851205
Reason: stable/xena branch of openstack/nova is about to be deleted. To be able to do that, all open patches need to be abandoned. Please cherry pick the patch to unmaintained/xena if you want to further work on this patch.