Cannot delete attachment for an orphan volume

[Liang Fang]

When the attached instance is lost, the related cinder volume will be orphan and cannot be delete any more. This may happen when the instance is removed but this information hadn't been transferred to cinder, e.g. maybe network issue. User is not able to delete the orphan volume because there're still some attachment with it. So user need to remove the attachment for the volume first.

The issue is: when user try to remove the attachment by click the button "Manage Attachments" for the orphan volume, GUI just shows: "Error: Unable to retrieve volume information. ", and cannot open the "Manage Attachments" dialog.

Some info may help for this bug:
To list the attachment: python-cinderclient\cinderclient\v3\attachments.py:VolumeAttachmentManager:list()
To delete an attachment: python-cinderclient\cinderclient\v3\attachments.py:VolumeAttachmentManager:delete()

[Lisa Li (lisali)]

More info please see https://bugs.launchpad.net/cinder/+bug/1791213 .
Expected results:
Horizon should be able to list volume attachment and allow users to delete.

[Akihiro Motoki (amotoki)]

There are questions to fix the bug. Can you clarify them?

* Should we use the Cinder Attachment API only when an attached VM has gone?
* What happens if the Cinder Attachment Delete API is used when an attached VM works well. Does Cinder API handle VM attachment as well? Otherwise, horizon should know more detail context to determine which API (of Nova and Cinder) should be called. How can horizon determine it?

Ivan is more familiar with Cinder so perhaps Ivan will know more than me.