Havana libvirt live migration should not be allowed without shared storage, even for volume-backed VMs

[Nikola Đipanov]

The following patch related to bug #1074054 https://review.openstack.org/#/c/17118/ mistakenly allows live migration without shared storage, if the instance is volume backed - only in the libvirt driver.

Bug #1235182 made this issue visible.

this is not the correct thing to do because even though the instance root disk is a cinder volume - the instance might have additional disks that need to be migrated. Currently - nova would just create them on the destination node.

Two possible solutions are:

1) Prevent non-block live migration without shared storage - effectively reverting https://review.openstack.org/#/c/17118/
2) Allow live migration ONLY for volume backed instances that have no local disks. This might be a preferred way of solving the issue, as there is value in having the flexibility to have live migrations without the overhead of setting up shared storage for volume-only VMs

[Edward Hope-Morley (hopem)]

non-local ephemeral disk support was recently added to Nova (https://review.openstack.org/#/c/36042/24) so I think there is a valid case for allowing live-migration without having shared storage on compute nodes.

[Nikola Đipanov (ndipanov)]

In reply to Edwaeds comment #1:

Most of the issues around this were discussed on the review that brought this bug to light: https://review.openstack.org/#/c/49816/ so anyone interested should consider reading through that as well.

[Russell Bryant (russellb)]

https://review.openstack.org/#/c/50982/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/50982
Committed: http://github.com/openstack/nova/commit/cf89e78a1b921adee5b1943600315b0637fdefdc
Submitter: Jenkins
Branch: master

commit cf89e78a1b921adee5b1943600315b0637fdefdc
Author: Nikola Dipanov <email address hidden>
Date: Thu Oct 10 16:00:26 2013 +0200

    Libvirt: disallow live-mig for volume-backed with local disk

    This patch makes libvirt raise an error if a live migration was
    requested without shared storage for a volume-backed instance, if that
    instance has any local disks.

    The reason is that without shared storage, local disks will be
    re-created on the destination node which can result in loss of data.

    Change-Id: Ic96dabf6020e957309280862b325792faf44b1f5
    Closes-bug: 1236356

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: milestone-proposed
Review: https://review.openstack.org/51316

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/51316
Committed: http://github.com/openstack/nova/commit/c63f4af000af191a9a70b6b62dbda40a5c9b59e5
Submitter: Jenkins
Branch: milestone-proposed

commit c63f4af000af191a9a70b6b62dbda40a5c9b59e5
Author: Nikola Dipanov <email address hidden>
Date: Thu Oct 10 16:00:26 2013 +0200

    Libvirt: disallow live-mig for volume-backed with local disk

    This patch makes libvirt raise an error if a live migration was
    requested without shared storage for a volume-backed instance, if that
    instance has any local disks.

    The reason is that without shared storage, local disks will be
    re-created on the destination node which can result in loss of data.

    Change-Id: Ic96dabf6020e957309280862b325792faf44b1f5
    Closes-bug: 1236356
    (cherry picked from commit cf89e78a1b921adee5b1943600315b0637fdefdc)