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

Christopher Yeoh cbkyeoh at gmail.com
Fri Mar 21 09:04:13 UTC 2014

On Thu, 20 Mar 2014 15:45:11 -0700
Dan Smith <dms at danplanet.com> wrote:
> I know that our primary delivery mechanism is releases right now, and
> so if we decide to revert before this gets into a release, that's
> cool. However, I think we need to be looking at CD as a very important
> use-case and I don't want to leave those folks out in the cold.

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.


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