[openstack-dev] [nova] Backwards incompatible API changes

Thierry Carrez thierry at openstack.org
Fri Mar 21 11:00:00 UTC 2014

Christopher Yeoh wrote:
> I don't want to cause issues for the CD people, but perhaps it won't be
> too disruptive for them (some direct feedback would be handy). The
> initial backwards incompatible change did not result in any bug reports
> coming back to us at all. If there were lots of users using it I think
> we could have expected some complaints as they would have had to adapt
> their programs to no longer manually add the flavor access (otherwise
> that would fail). It is of course possible that new programs written in
> the meantime would rely on the new behaviour.
> I think (please correct me if I'm wrong) the public CD clouds don't
> expose that part of API to their users so the fallout could be quite
> limited. Some opinions from those who do CD for private clouds would be
> very useful. I'll send an email to openstack-operators asking what
> people there believe the impact would be but at the moment I'm thinking
> that revert is the way we should go.
>> Could we consider a middle road? What if we made the extension
>> silently tolerate an add-myself operation to a flavor, (potentially
>> only) right after create? Yes, that's another change, but it means
>> that old clients (like horizon) will continue to work, and new
>> clients (which expect to automatically get access) will continue to
>> work. We can document in the release notes that we made the change to
>> match our docs, and that anyone that *depends* on the (admittedly
>> weird) behavior of the old broken extension, where a user doesn't
>> retain access to flavors they create, may need to tweak their client
>> to remove themselves after create.
> My concern is that we'd be digging ourselves an even deeper hole with
> that approach. That for some reason we don't really understand at the
> moment, people have programs which rely on adding flavor access to a
> tenant which is already on the access list being rejected rather than
> silently accepted. And I'm not sure its the behavior from flavor access
> that we actually want.
> But we certainly don't want to end up in the situation of trying to
> work out how to rollback two backwards incompatible API changes.

My vote still goes to reverting, for all the reasons Chris just exposed.
I could live with the middle road though... My main concern is to avoid
breaking release followers with an issue we detected pre-release.

Thierry Carrez (ttx)

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