Ghanshyam Mann

On Mon, Feb 15, 2016 at 12:07 PM, Alex Xu <> wrote:
> If we support 2.x.y, when we bump 'x' is a problem. We didn't order the API
> changes for now, the version of API change is just based on the order of
> patch merge. For support 2.x.y, we need bump 'y' first for back-compatible
> changes I guess.
> As I remember, we said before, the new feature is the motivation of user
> upgrade their client to support new version API, whatever the new version is
> backward compatible or incompatible. So I guess the initial thinking we hope
> user always upgrade their code than always stop at old version? If we bump
> 'x' after a lot of 'y', will that lead to user always stop at 'x' version?
> And the evolution of api will slow down.
> Or we limit to each release cycle. In each release, we bump 'y' first, and
> then bump 'x'. Even there isn't any back-incompatible change in the release.
> We still bump 'x' when released. Then we can encourage user upgrade their
> code. But I still think the back-incompatible API change will be slow down
> in development, as it need always merged after back-compatible API change
> patches.

Yea that true and will be more complicated from development
perspective which leads to slow down the evolution of API changes.
But if we support x.y then still we can change x at any time back
in-comp changes happens(i mean before y also)? Or I may not be getting
the issue you mentioned about always bump y before x.

I like the idea of distinguish the backward comp and in-comp changes
with x and y which always gives clear perspective about changes.
But it should not lead users to ignore y. I mean some backward comp
changes which are really good gets ignored by users as they start look
at the x only.
For example- "adding attribute in resource representation" is back
comp change (if so) and if that is added as y then, it might get
ignored by users.

Another way to clearly distinguish backward comp and in-comp changes
is through documentation which was initially discussed during
microversion specs. Currently doc has good description about each
changes but not much clear way about backward comp or not.
Which we can do by adding a clear flag [Backward Compatible/
Incompatible] for each version in doc [1]-

> 2016-02-13 4:55 GMT+08:00 Andrew Laski <>:
>> Starting a new thread to continue a thought that came up in
>> The Nova API microversion framework allows for backwards compatible and
>> backwards incompatible changes but there is no way to programmatically
>> distinguish the two. This means that as a user of the API I need to
>> understand every change between the version I'm using now and a new
>> version I would like to move to in case an intermediate version changes
>> default behaviors or removes something I'm currently using.
>> I would suggest that a more user friendly approach would be to
>> distinguish the two types of changes. Perhaps something like 2.x.y where
>> x is bumped for a backwards incompatible change and y is still
>> monotonically increasing regardless of bumps to x. So if the current
>> version is 2.2.7 a new backwards compatible change would bump to 2.2.8
>> or a new backwards incompatible change would bump to 2.3.8. As a user
>> this would allow me to fairly freely bump the version I'm consuming
>> until x changes at which point I need to take more care in moving to a
>> new version.
>> Just wanted to throw the idea out to get some feedback. Or perhaps this
>> was already discussed and dismissed when microversions were added and I
>> just missed it.
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