[openstack-dev] [Nova] Concrete Proposal for Keeping V2 API

Christopher Yeoh cbkyeoh at gmail.com
Tue Mar 4 06:35:01 UTC 2014

On Mon, 03 Mar 2014 12:32:04 -0500
Russell Bryant <rbryant at redhat.com> wrote:

> There has been quite a bit of discussion about the future of the v3
> API recently.  There has been growing support for the idea that we
> should change course and focus on evolving the existing v2 API
> instead of putting out a new major revision.  This message is a more
> complete presentation of that proposal that concludes that we can do
> what we really need to do with only the v2 API.

So one thing which I think is relevant to this discussion is that we
are not comparing two theoretical paths. On one hand we have a
v2 API related proposal which involves lot of backporting. I think
there is a lack of appreciation in this proposal over how much effort
would be involved to achieve this (and I don't think anyone is really
putting their hand up to do the work required in the long term) as well
as the risk involved in accidental changes to the V2 API. As a very
rough guide of effort I think around 400+ patches have merged (not
include copy/paste part 1 type patches) just in the Nova tree for the
V3 API over Havana and Icehouse. This does not count the python
novaclient or tempest support which would have to be implemented at
some point to support an API changes which were backported.

On the other hand we have the V3 API which with the exception of the
nova-network support is almost complete and merged. And we have a much
better idea of the effort as well as several people who want to and
have the time to work on it as well as being willing to help reduce the
dual maintenance overhead.

To try to clarify what the V3 API would mean for users, developers and
deployers I have put some information together here:


It also covers some approaches for reducing the dual maintenance issues
in the short term and removing them in the long term. As well as a
possible strategy for long term handling of significant API changes.

Although having a V3 API does certainly involve some dual maintenance
concerns about making internal Nova changes whilst supporting both the
V2 and V3 API code. And so far in this discussion I don't think we
have really managed to quantify what the dual maintenance overhead
actually is (although the document above tries to).

Also I don't think we should ignore the extra maintenance burdens
discussed in in the linked document of attempting to evolve the V2
API and keep the old V2 API code base (which I think we may be
able to separate conceptually from keeping support for the V2 API).


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