After attachment-delete nova still sees volume as attached

[Facundo Ciccioli]

Using cinder attachment-delete command to detach a volume from a stopped instance seems to be affecting only what cinder sees but not what nova sees.

Here are rough steps to reproduce:

1. Create a volume from an image, say the volume's UUID is $VOL

2. Create an instance using that volume as storage:

    $ openstack server create --volume $VOL --flavor some_flavor test-instance

3. Verify the volume is attached to the instance:

    $ openstack server show test-instance -fvalue -cvolumes_attached
    id='$VOL'

4. Get the attachment id using, suppose it's $ATT:

    $ os volume show $VOL -fvalue -c attachments | python -c 'import sys,pprint;pprint.pprint(eval(sys.stdin.read()))'
    [{'attached_at': '2021-02-02T09:38:02.000000',
      'attachment_id': '$ATT',
      'device': '/dev/vda',
      'host_name': 'some-hostname',
      'id': '$VOL',
      'server_id': '...',
      'volume_id': '$VOL'}]

5. Stop the instance

6. Detach the volume:

    $ cinder --os-volume-api-version 3.50 attachment-delete $ATT

Now the volume will show as not being attached according to openstack volume show:

    $ os volume show $VOL -fvalue -c attachments | python -c 'import sys,pprint;pprint.pprint(eval(sys.stdin.read()))'
    []

But it will still be listed as volumes_attached by server show:

    $ openstack server show test-instance -fvalue -cvolumes_attached
    id='$VOL'

I believe this to be related with the fact that the volume being a boot device, it cannot actually be detached. This indeed happens is I try to remove the volume by means of the openstack CLI:

    $ os server remove volume test-instance $VOL
    Cannot detach a root device volume (HTTP 403) (Request-ID: req-...)

I think cinder should error in the same way.

[Sofia Enriquez (lsofia-enriquez)]

This looks like the right behaviour.
If you delete the attachment from Cinder and don't detach from Nova, this is what you would expect to happen.