[openstack-dev] Quantum + ZeroMQ (with a sprinkling of Nova) in Folsom

Mark McLoughlin markmc at redhat.com
Tue Sep 25 20:45:31 UTC 2012

On Tue, 2012-09-25 at 13:28 -0400, Eric Windisch wrote:
> Russell, perhaps. The issue is that if the message format changes, it
> would be lower cost to do it now. Also, I'm moving this to the public
> list, because I agree that it is a good time to do it. 
> IF there is an RC3 for Nova, I'd like for consideration to get the
> message-format change in, because it reduces complexity for Grizzly
> (having to understand two formats), and because it will make the
> Quantum code supportable. This binary needs to move outside of Nova to
> avoid this unnecessary interdependency.
> It might be resolvable by adding a version to the message format, but
> it doesn't solve the problem today - which, arguably, doesn't have to
> be solved. We can just release with the zeromq stuff broken in Quantum
> for Folsom, without any ability to backport, and I'm prepared for that
> to happen. I've just rallied for a best-effort to get it in, because
> it would be a nice to have, after finding out at F3 that it wouldn't
> work.
> As it is, the patch that is already in Quantum should be enough to get
> us going for Folsom if we can also get the patch into Nova. The two
> patches pending review can be backported, if necessary. 

It took me a while to make any sense of this

This change which was merged into openstack-common a few days ago:


is what changed the message format?

I must admit I didn't realize there was a backwards compatibility issue
with that patch.

So, the message format used by zmq in Nova is incompatible with what's
used in Quantum.

At this point I'd be inclined to document the zmq driver as unstable and
warn users that it's only included in Folsom as a "preview". Making
incompatible changes days before the release should tell us that we're
not ready to commit to maintaining compatibility with this driver yet.

If we don't document it as unstable, we have two choices before the
final Folsom release - either merge the new format into Nova or revert
it from Quantum.


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