[openstack-dev] [nova] nova-manage cell_v2 map_instances uses invalid UUID as marker in the db

Dan Smith dms at danplanet.com
Thu May 10 18:48:31 UTC 2018

> The oslo UUIDField emits a warning if the string used as a field value
> does not pass the validation of the uuid.UUID(str(value)) call
> [3]. All the offending places are fixed in nova except the nova-manage
> cell_v2 map_instances call [1][2]. That call uses markers in the DB
> that are not valid UUIDs.

No, that call uses markers in the DB that don't fit the canonical string
representation of a UUID that the oslo library is looking for. There are
many ways to serialize a UUID:


The 8-4-4-4-12 format is one of them (and the most popular). Changing
the dashes to spaces does not make it not a UUID, it makes it not the
same _string_ and it's done (for better or worse) in the aforementioned
code to skirt the database's UUID-ignorant _string_ uniqueness

> If we could fix this last offender then we could merge the patch [4]
> that changes the this warning to an exception in the nova tests to
> avoid such future rule violations.
> However I'm not sure it is easy to fix. Replacing
> '00000000-0000-0000-0000-00000000' might work

The project_id field on the object is not a UUIDField, nor is it 36
characters in the database schema. It can't be because project ids are
not guaranteed to be UUIDs.

> but I don't know what to do with instance_uuid.replace(' ', '-') [2]
> to make it a valid uuid. Also I think that if there is an unfinished
> mapping in the deployment and then the marker is changed in the code
> that leads to inconsistencies.

IMHO, it would be bad to do anything that breaks people in the middle of
a mapping procedure. While I understand the desire to have fewer
spurious warnings in the test runs, I feel like doing anything to impact
the UX or performance of runtime code to make the unit test output
cleaner is a bad idea.

> I'm open to any suggestions.

We already store values in this field that are not 8-4-4-4-12, and the
oslo field warning is just a warning. If people feel like we need to do
something, I propose we just do this:


It is one of those "we normally wouldn't do this with object schemas,
but we know this is okay" sort of situations.

Personally, I'd just make the offending tests shut up about the warning
and move on, but I'm also okay with the above solution if people prefer.


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