[Openstack] WADL [was: v3 API draft (update and questions to the community)]
Doug Davis
dug at us.ibm.com
Fri Jun 15 12:35:32 UTC 2012
I don't see this as an either-or type of thing.
Totally agree with Mark that the APIs need to be more clearly documented
and that should be independent of any kind of IDL (ala WADL) artifact. I
say this mainly because I think we always need to have something that's
human readable and not machine readable. There will always be semantics
that can not be expressed via the machine readable artifacts. Having said
that, there are people that like to have IDL-like artifacts for some kind
of tooling. So, along with the well-documented APIs should be whatever
artifacts that can makes people's lives easier. This means XSD, WASL,
WSDL, etc... whatever - pick your favorite.
No matter what artifact you choose to use to guide your coding (even if
its just the "well documented human readable API doc"), you're still bound
to that particular version of the APIs. Which means a change in the
APIs/server-code might break your client. In this respect I don't think
WADL or docs are more or less brittle than the other. To me the key
aspects are the extensibility points. Once the APIs are deemed 'stable',
we just need to make sure that new stuff is backwards compatible which
usually means defining and leveraging well placed extensibility points.
thanks
-Doug
______________________________________________________
STSM | Standards Architect | IBM Software Group
(919) 254-6905 | IBM 444-6905 | dug at us.ibm.com
The more I'm around some people, the more I like my dog.
Mark Nottingham <mnot at mnot.net>
Sent by: openstack-bounces+dug=us.ibm.com at lists.launchpad.net
06/14/2012 08:20 PM
To
"Nguyen, Liem Manh" <liem_m_nguyen at hp.com>
cc
"openstack at lists.launchpad.net" <openstack at lists.launchpad.net>
Subject
[Openstack] WADL [was: v3 API draft (update and questions to the
community)]
Hi Liem,
I'm one of the folks who helped Marc get WADL off of the ground. At the
time, my use cases were exactly as you describe: documentation (e.g., <
https://github.com/mnot/wadl_stylesheets>) and testing.
Even back then, there was a lot of discussion in the community; e.g., see:
http://bitworking.org/news/193/Do-we-need-WADL
http://old.nabble.com/Is-it-a-good-idea-to-make-your-WADL-available--tc6087155r1.html
http://www.25hoursaday.com/weblog/CommentView.aspx?guid=f88dc5a6-0aff-44ca-ba42-38c651612092
I think many of the concerns that were expressed then are still valid --
some even within these limited uses. In no particular order:
* People can and will use WADL to represent a "contract" to a service
(really, an IDL), and "bake" client code to a snapshot of it in time.
While it's true that the client and server need to have agreement about
what goes on the wire and what it means, the assumptions around what
guarantees WADL makes are not well-thought-out (in a manner similar to
WSDL), making clients generated from it very tightly bound to the snapshot
of the server they saw at some point in the past. This, in turn, makes
evolution / extension of the API a lot harder than it needs to be.
* WADL's primitives are XML Schema datatypes. This is a horrible match for
dynamic languages like Python.
* WADL itself embodies certain patterns of use that tend to show through
if you design for it; these may or may not be the best patterns for a
particular use case. This is because HTTP and URLs are very flexible
things, and it isn't expressive enough to cover all of that space. As a
result, you can end up with convoluted APIs that are designed to fit WADL,
rather than do the task at hand.
>From what I've seen, many developers in OpenStack are profoundly
uninterested in working with WADL. YMMV, but AFAICT this results in the
WADL being done by other folks, and not matching the reality of the
implementation; not a good situation for anyone.
What we need, I think, is a specification of the API that's precise,
unambiguous, and easy to understand and maintain. I personally don't think
WADL is up to that task (at least as a primary artefact), so (as I
mentioned), I'm going to be proposing another approach.
Cheers,
On 15/06/2012, at 2:08 AM, Nguyen, Liem Manh wrote:
> IMHO, a well-documented WADL + XSD would say a thousand words (maybe
more)... And can serve as a basis for automated testing as well. I
understand that the v3 API draft is perhaps not at that stage yet; but,
would like to see a WADL + XSD set as soon as the concepts are solidified.
>
> Liem
>
> -----Original Message-----
> From: openstack-bounces+liem_m_nguyen=hp.com at lists.launchpad.net
[mailto:openstack-bounces+liem_m_nguyen=hp.com at lists.launchpad.net] On
Behalf Of Mark Nottingham
> Sent: Tuesday, June 12, 2012 8:43 PM
> To: Gabriel Hurley
> Cc: openstack at lists.launchpad.net
> Subject: Re: [Openstack] [keystone] v3 API draft (update and questions
to the community)
>
>
> On 13/06/2012, at 1:24 PM, Gabriel Hurley wrote:
>
>> Totally agree with all of Jay's points, and I also couldn't agree more
with Mark on the importance of being crystal clear, and not operating on
just a "common understanding" which is quickly misunderstood or forgotten.
>>
>> Ideally I'd like to see an OpenStack API feature contract of some
sort... essentially a document describing the FULL list of features, how
those parameters are controlled and how they would interact, and what a
project should do if they do not implement an API feature (hopefully only
for technical reasons such as Keystone paging with LDAP or swift with
complex DB-esque operations). This isn't saying we should have a unified
API spec, I'm talking solely about a contract for the features all APIs
should strive to support.
>>
>> This would be a big project, but everyone would then have a common
agreement about what the user experience of interacting with OpenStack
should be. The project APIs as they stand are siloed and stunningly
inconsistent, and I'd love to work toward fixing that.
>
> Absolutely.
>
> One of my other projects is to rewrite the API as a proper specification
(in a style similar to an Internet-Draft, not that we'd necessarily
publish it as one).
>
> I should have something to show soon; if you're interested in helping
out, that'd be great.
>
> Cheers,
>
>
>> My two cents,
>>
>> - Gabriel
>>
>>> -----Original Message-----
>>> From: openstack-bounces+gabriel.hurley=nebula.com at lists.launchpad.net
>>> [mailto:openstack-
>>> bounces+gabriel.hurley=nebula.com at lists.launchpad.net] On Behalf Of
>>> Mark Nottingham
>>> Sent: Tuesday, June 12, 2012 7:20 PM
>>> To: Jay Pipes
>>> Cc: openstack at lists.launchpad.net
>>> Subject: Re: [Openstack] [keystone] v3 API draft (update and questions
to
>>> the community)
>>>
>>>
>>> On 13/06/2012, at 3:31 AM, Jay Pipes wrote:
>>>
>>>> This isn't necessarily true. Nova's compute layer goes through a
number of
>>> steps to ensure a semi-transactional nature to certain operations like
>>> resizing. Certain times a query needs to indicate that it intends to
make a
>>> reservation of resources (see quota/reservation system now .. this is
the
>>> SELECT FOR UPDATE paradigm) and other times, the query doesn't care
>>> about such things. In the latter case, there aren't expectations that
the list
>>> returned is 100% accurate according to the state of the database at a
>>> particular timestamp of when the transaction occurred. In this case,
filters
>>> and optimistic pagination works perfectly fine, IMHO.
>>>
>>> That might work, but we need to be crystal-clear about the semantics
of
>>> what we're giving back; having it understood between OpenStack
projects
>>> isn't good enough.
>>>
>>> I.e., we're not building the APIs just for Horizon; they're for lots
of folks, and
>>> subtle semantics -- even when well-documented, much less when they're
>>> not -- are often misunderstood.
>>>
>>> Cheers,
>>>
>>> --
>>> Mark Nottingham http://www.mnot.net/
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> Mailing list: https://launchpad.net/~openstack
>>> Post to : openstack at lists.launchpad.net
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>>
>>
>>
>> _______________________________________________
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>
> --
> Mark Nottingham http://www.mnot.net/
>
>
>
>
> _______________________________________________
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--
Mark Nottingham http://www.mnot.net/
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