[openstack-dev] [nova] Supporting force live-migrate and force evacuate with nested allocations

Eric Fried openstack at fried.cc
Tue Oct 9 21:01:24 UTC 2018

On 10/09/2018 02:20 PM, Jay Pipes wrote:
> On 10/09/2018 11:04 AM, Bal√°zs Gibizer wrote:
>> If you do the force flag removal in a nw microversion that also means
>> (at least to me) that you should not change the behavior of the force
>> flag in the old microversions.
> Agreed.
> Keep the old, buggy and unsafe behaviour for the old microversion and in
> a new microversion remove the --force flag entirely and always call GET
> /a_c, followed by a claim_resources() on the destination host.
> For the old microversion behaviour, continue to do the "blind copy" of
> allocations from the source compute node provider to the destination
> compute node provider.

TBC, for nested/sharing source, we should consolidate all the resources
into a single allocation against the destination's root provider?

> That "blind copy" will still fail if there isn't
> capacity for the new allocations on the destination host anyway, because
> the blind copy is just issuing a POST /allocations, and that code path
> still checks capacity on the target resource providers.

What happens when the migration fails, either because of that POST
/allocations, or afterwards? Do we still have the old allocation around
to restore? Cause we can't re-figure it from the now-monolithic
destination allocation.

> There isn't a
> code path in the placement API that allows a provider's inventory
> capacity to be exceeded by new allocations.
> Best,
> -jay
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