On 11/30/2012 06:23 AM, Martyn Taylor wrote:
On 11/30/2012 01:43 PM, Jiří Stránský wrote:
On 29.11.2012 00:12, Richard Su wrote:
Hi,
I'm going to start the discussion on versioning. After some
research, a question that I think we should be asking first is does
the API need to be versioned at all? Or what do we mean by versioning?
I think there are two initial paths. Do we build the API so that it
is backwards compatible so that existing clients continue to work as
the api evolves in future conductor releases? Or is this not tenable
and we should prepare for the inevitable change that will break
backwards compatibility and introduce a versioning scheme?
* Backwards Compatibilty
Leaving discussions about Heat and CIMI aside (which look to be
layers on top of a base Conductor API) and if we think our existing
models are correct and are stable I think maintaining backwards
compatibillity would be the simplest course. This means that once
we've released an API, changes should be additive; removing
attributes or elements is not allowed. It also means we never remove
ways of interacting with the API. If we add a new field to a
resource, to maintain compatibility with existing clients it should
be possible to create the resource without specifying the new field.
We would indicate the version of the API in a header so that the
client knows which version it is taking to. And changes to the API
will be documented as each version if released. But there is no
effort here to make multiple versions of the API available through a
HTTP header or URI off of the same Conductor instance.
* Versioning
A while ago we committed to having the API work off the same
controller as the UI. If we decide that the API must be versioned, I
think we will need to break the API off to its own controllers.
From what I have gathered, most versioning schemes use a namespace
to denote a version and each namespace has its own controllers,
views, and tests. A new API version would mean copying the current
namespace/version into a new directory with its own controllers,
view, and tests. There are some gems like Versionist or Rocket Pants
to ease versioning. What is not clear to me though is if there is a
significant modeling change how would one make different versions of
the API continue to work off of the same Conductor instance.
Is there a particular requirement that requires us to version the
API? I think there will be significant work involved if we do choose
to version the API. Is it worth the effort?
Or is there some other type of versioning people are thinking about?
Your thoughts?
We already know we can't keep compatibility with API that's now in
use. When Tim comes, the image management API will change. One could
say we will have a "v2 API" in place. And we won't provide backwards
compatibility or let the client choose which API version it wants to
use. Letting my mind wonder into the hypothetical future - Conductor
can develop in a way that we can have this "v2 API" in place for some
(hopefully a long) time, but eventually we might have to change the
API again into "v3 API".
So, my 2 cents: I don't want to serve multiple API versions from one
Conductor instance, I want to stick to backwards compatibility as
much as possible, but I'd like to provide version information with
the API and have clients indicate what version they expect to
communicate with. When we absolutely have to make changes (hopefully
once in a few years), we make them all at once and increment the API
version.
In an ideal world, we would stick to being backwards compatible like
CIMI or Deltacloud, but I don't think this is possible for Conductor,
given the amount of evolution. Also we would have to be much, much
more careful about introducing new fields in API than we are right
now ... which we should be anyway :) (Thinking of the discussion
about deployables #show we are having, which also applies to
instances API. I'm sorry I didn't make the time to go through the API
RFC properly and raise my objections earlier.)
Take care,
J.
This gets a +1 from me. We do not* want to support multiple versions
of the API in the foreseeable future. Our API is too unstable right
now. Once we have a stable API then we can think about it, possibly
having some support period for the previous version. Until then
though, I think a general policy amongst the team of trying to
maintain backwards compatibility as much as possible and having a way
to determine the API version should be sufficient. The version in the
entry point URL v Content Type gets my vote.
Thanks
Martyn
------
Resources I found useful:
1. http://watzmann.net/blog/2012/08/rest-api-evolution.html
2. http://www.mnot.net/blog/2011/10/25/web_api_versioning_smackdown
3.
http://fedoraproject.org/wiki/Cloud_APIs_REST_Style_Guide#Compatibility_and_Versioning
4. http://railscasts.com/episodes/350-rest-api-versioning
To wrap up this discussion, the conclusion here is that we will maintain
backwards compatibility and not support multiple versions of the API in
the same Conductor instance. We will embed a version number so that
clients can determine which version of the API they are speaking to.
If have any concerns about this approach, please speak up.
Thanks,
Richard
