Live migration of instances requires the destination AND the source to have the same resources free on top of what the instance is taking

[Diko Parvanov]

A live-migration of a VM with 8 vCPUs from host SOURCE to host DEST, where host SOURCE has no free vCPUs will fail, because it will require that host SOURCE has 8 vCPUs together with the already allocated 8 vCPUs from the running instance, so it requires the source host to have 16 vCPUs.

The workaround is to increase the allocation ratio of the host SOURCE via openstack resource provider inventory class set --allocation_ratio and then scale it back down to the required value.

[sean mooney (sean-k-mooney)]

currently we do not have enough info to traige this so setting to incomplete

what version of OpenStack was this observed with.
i believe live migration should be using multiple allocations in placement
one for the source host and a second of the dest using the migration uuid

[Diko Parvanov (dparv)]

cloud is focal/ussuri, it is using multiple allocations, but nova should not require the source host to have twice the machine of available resources

[Balazs Gibizer (balazs-gibizer)]

I tried to reproduce the described bug but I was not able to. See [1].

Please note that it is a known behavior that if the source compute is _overallocated_ (i.e. used > total*allocation_ratio - reserved) then you cannot move the VM out from that host. But If the source compute is just full, then you should be able to migrate the VM as [1] shows.

Could you please provide:
* openstack resource provider inventory list <source_compute_node_uuid>
* openstack resource provider inventory list <dest_compute_node_uuid>
* openstack resource provider usage show <source>
* openstack resource provider usage show <dest>
* openstack resource provider allocation show <vm uuid>
* openstack server event list <vm uuid>

Also please provider the relevant nova and placement logs please.

Setting this as Incomplete as I cannot reproduce the issue.

[1] https://review.opendev.org/c/openstack/nova/+/845168

[Launchpad Janitor (janitor)]

[Expired for OpenStack Compute (nova) because there has been no activity for 60 days.]