[openstack-dev] [Ironic] Let's talk about API versions

Clint Byrum clint at fewbar.com
Tue Jul 28 01:09:37 UTC 2015

Excerpts from Jim Rollenhagen's message of 2015-07-27 13:35:25 -0700:
> Hi friends.
> Ironic implemented API "micro" versions in Kilo. We originally did this
> to allow for breaking changes in the API while allowing users to opt in
> to the breakage.
> Since then, we've had a "default version" for our client that we bump to
> something sensible with each release. Currently it is at 1.8.
> Negotiation is done with the server to figure out what is supported and
> adjust accordingly.
> Now we've landed a patch[0] with a new version (1.11) that is not
> backward compatible. It causes newly added Node objects to begin life in
> the ENROLL state, rather than AVAILABLE. This is a good thing, and
> people should want this! However, it is a breaking change. Automation
> that adds nodes to Ironic will need to do different things after the
> node-create call.
> Our API versioning scheme makes this opt-in (by specifying the API
> version). However, some folks have a problem with releasing this change
> as-is. The logic is that we might release a client that defaults to 1.11
> or higher, or the user may request 1.12 later to get a new feature, thus
> breaking their application that enrolls nodes.
> This is clearly backwards. Users should read release notes and be aware
> of what changes between versions in the API. Users need to be aware of
> the fact that our API is versioned, and use that to their advantage.
> It seems to me that the goal of the version negotiation in our client
> has been to pretend that our API versions don't exist, from a user
> perspective. We need to stop doing this and force users to think about
> what they are doing when they interact with our API.
> It seems to me we have a few options here:
> 1) Default the python client and CLI to the earliest supported version.
> This will never break users by default.
> 2) Default the python client and CLI to use the special version
> 'latest'. This will always use the latest API version, and always
> break people when a new server version (that is not backwards
> compatible) is deployed.
> 3) Do what Nova does[1]. Default CLI to latest and python client to
> earliest. This assumes that CLI is typically used for one-time commands
> (and it isn't a big deal if we break a one-off command once), and the
> python client is used for applications.
> 4) Require a version to use the client at all. This would be a one-time
> break with how applications initialize the client (perhaps we could fall
> back to the earliest version or something for a deprecation period).
> This isn't a great user experience, however, it's the best way to get
> users to think about versioning. And no, "this requires typing another
> argument every time!" is not a valid argument against this; we already
> require a number of arguments, anyone sane doesn't type --ironic-api-url
> or --os-username every time they use the client.
> 5) Do what we're doing now. Bump the client's default version with every
> release. This mostly hides these versions from end users, and in general
> those users probably won't know they exist. And then we run into
> arguments every time we want to make a breaking change to the API. :)

Could you combine 1 and 4?

Deprecate not specifying the version, but pin to the oldest one for now?
That way users get the warnings that they need to adapt, but things keep
working? Could be switched to just 4 after a few months.

I say that having just added some IP addresses to a server with iproute2,
which has been telling me for probably 10 years that _not_ adding /32
to single IP's will eventually be deprecated...

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