Checking the bug report you mentioned and seems the best solution will be rely on that BP you mentioned
in the report. I sugguest one thing we can do is that we mention that we will not reset the tag but it might
not working. And when we can support assign tag when attach volume to shelved_offloaded instances,
we then perform the reset and update action. 

On Thu, Feb 28, 2019 at 10:10 AM Matt Riedemann <mriedemos@gmail.com> wrote:
On 2/27/2019 7:41 PM, Zhenyu Zheng wrote:
> There is something I don't quite understand, what will be different for
> the volumes that are newly attached and
> the existing volumes in case you mentioned? I mean, the existing volumes
> could also have tags, and when
> we unshelve,  we still have to handle the tags in bdms, no matter it is
> existing bdms or newly atteched when the
> instance is in ``shelved_offloaded`` status. What is the difference?

There isn't, it's a bug:

https://bugs.launchpad.net/nova/+bug/1817927

Which is why I think we should probably lift the restriction in the API
so that users can attach volumes with tags to a shelved offloaded instance.

I'm not really comfortable with adding root volume detach/attach support
if the user cannot specify a new tag when attaching a new root volume,
and to do that we have to remove that restriction on tags + shelved
offloaded servers in the API.

--

Thanks,

Matt