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To be clear, the idea of the decorator and the base code comes from Nova, but it is not the Nova implementation. I didn't just copy the code over, that wouldn't have worked. What I liked from the Nova implementation was the decorator.  Vijendar and I went through several different projects(Ironic, Keystone, Nova, etc...) looking for examples of how we wanted to implement this. We POC'ed a couple of them to compare.  The decorator method of organizing and labeling was the one we liked best from a future development point of view. It kept the API code easy to read and easy to understand what code belonged to each microversion.  I took the structure and some of the code from Nova and then changed it to work for Pecan.  Nova's implementation was mixed into their WSGI code and we don't need to recreate that since we use pecan in magnum. So the concern of the complexity of the nova router is not really part of this. Take a look at the code review, I feel the code is not too complex and provides additional error checking that we would have to add to each method without it. 

Quick summary of how it works:
1) The decorators create a dictionary attaching method name to a list of available methods with version information.
2) That dictionary is added to the controller object
3) When a request comes in and Pecan selects the correct method needed for the API call, the controller  __getattribute__ call uses the dictionary to return the correct method based on the request version. It then returns the selected method and Pecan proceeds as before.

That said, if we really believe that we won't do more than a few microversion changes then I'll agreed that it might be not be critical that we have something like this. If that is what is decided, I can resubmit this with just the Version class updates and response header fixes. The microversion checking can then be done in each method as needed.

Jaycen


-----Original Message-----
From: taget [mailto:qiaoliyong at gmail.com] 
Sent: Thursday, July 28, 2016 6:46 PM
To: openstack-dev at lists.openstack.org
Subject: Re: [openstack-dev] [Magnum] Microversioning implementation

Hongbin & team

Please forget Semantic Versioning API, that should not be done in short term especially API WG had defined lots of Microversion API docs, sorry to make confusions.

Of cause that Microversion API is important to OpenStack, and it has documented well in API WG [1].
For Magnum, I remember that the implementation idea is from ironic [2], it is simple.

For [3] which comes from Nova is complex because that nova implement router itself, but Magnum
(Ironic) use pecan. We need to maintain it Magnum as well, also when I doing some testing, I still find some unexpected exception if passing bad Microversion, it should follow API WG.

At last Magnum has very few APIs entry point now, baymodel.py bay.py certificate.py magnum_services.py

Seen from Ironic, it has bump the version to v1.21 [2] with current Magnum's microversion's infra

I am okay to go with [3] as long as [3] fellows up with APIWG[1] and have better testing, I really don't want to maintain an infra which won't be used frequently.

[1] https://wiki.openstack.org/wiki/VersionDiscovery
[2] https://github.com/openstack/ironic/blob/master/doc/source/webapi/v1.rst
[3]
https://review.openstack.org/#/c/343060/8/magnum/api/controllers/v1/bay.py


On 2016年07月29日 03:19, Hongbin Lu wrote:
> OK. My replies are inline.
>
>> -----Original Message-----
>> From: Grant, Jaycen V [mailto:jaycen.v.grant at intel.com]
>> Sent: July-28-16 2:31 PM
>> To: OpenStack Development Mailing List (not for usage questions)
>> Subject: Re: [openstack-dev] [Magnum] Microversioning implementation
>>
>> I was completely unaware of any discussion of Semantic Versioning.
>> That was brought up by Eli Qiao in the code review, so he might be the
>> one to point us in the right direction for that.
>>
>> Jaycen
>>
>> -----Original Message-----
>> From: Hongbin Lu [mailto:hongbin.lu at huawei.com]
>> Sent: Thursday, July 28, 2016 11:10 AM
>> To: OpenStack Development Mailing List (not for usage questions)
>> <openstack-dev at lists.openstack.org>
>> Subject: Re: [openstack-dev] [Magnum] Microversioning implementation
>>
>> Added this to the agenda of next team meeting [1].
>>
>> I would like to ask clarification for " the community are discussing to
>> using Semantic Versioning(X.Y.Z) instead of microversion X.Y ". Could
>> anyone provide more information about that?
>>
>> Best regards,
>> Hongbin
>>
>>> -----Original Message-----
>>> From: Grant, Jaycen V [mailto:jaycen.v.grant at intel.com]
>>> Sent: July-28-16 10:52 AM
>>> To: OpenStack Development Mailing List (not for usage questions)
>>> Subject: [openstack-dev] [Magnum] Microversioning implementation
>>>
>>>
>>> There has been a discussion around micro versioning implementation
>>> going on in the following patch:
>>> https://review.openstack.org/#/c/343060/8 and I was asked to bring it
>>> to the mailing list for further discussion.
>>>
>>> Magnum added header support for microversioning according to the
>>> Openstack spec[1] but since we haven’t had any changes yet it was not
>>> being used.  In the patch mentioned above I added code that provides
>>> infrastructure for implementing micro versions for our API methods.
>> I
>>> took the idea from how Nova implemented micro versioning and used
>> some
>>> of their code modified to work with Pecan.  The basic idea is that
>> you
>>> version a method using api_version decorator as shown below:
>>>
>>> @base.Controller.api_version("1.1")
>>>      @expose.expose(BayCollection, types.uuid)
>>>      def get_all(self, marker=None):
>>>          """Retrieve a list of bays.
>>> # code for version 1.1
>>>
>>> @base.Controller.api_version(“1.2”, “1.3")
>>> @expose.expose(BayCollection,
>>> types.uuid) def get_all(self, marker=None):
>>> """Retrieve a list of bays.
>>> # code for versions 1.2 through 1.3
>>>
>>> @base.Controller.api_version("1.4")
>>> @expose.expose(BayCollection, types.uuid) def get_all(self,
>>> marker=None):
>>> """Retrieve a list of bays.
>>> # code for version 1.4 to latest version
>>>
>>>
>>> The api_version code takes care of selecting the correct version
>> based
>>> on version requested in the header. It also checks for version
>>> overlaps in the methods and gaps in the method versions.
>>>
>>>
>>> While working on this Vijendar(working on the first api changes that
>>> need api versioning) and myself, evaluated several other alternatives:
>>>
>>> 1) Just have each method check the version object and handle the
>>> differences. This was the most basic solution and will work but we
>>> were concerned it would add a lot of duplicate code. We were also
>>> concerned it would be messy in the future as more and more micro
>>> versions were added. Each method would now be responsible for
>>> additional checking and more places to change code if there were
>>> overall micro version code changes in the future.
>>>
>>> 2) Separate pecan controllers for each micro version. When a new
>> micro
>>> version is added a new controller would be created inheriting from
>> the
>>> previous version controller. The new controller would override the
>>> modified methods. Routing changes would be added to make sure that
>> the
>>> correct controller was used depending on the API header.  We felt
>> that
>>> the api_version decorator was slightly less complicated and less code
>>> overhead on each api version change.
>>>
>>> I’d appreciate feedback on whether this is the right way to go or if
>>> it would be better to go to alternative option 1 or 2. Here were some
>>> of the concerns by one of the cores in the code review:
>>>
>>>      I don't accept this patch, mark it as -2:
>>>      Reason:
>>>      1. we have already support microversion in our code base, and
>> your
>>> propose (copied from nova) make things complicated.
>>>      2. I think you want to support "Support for async bay operations"
>>> for you    adding microversion support, right?
>>>      I would like suggest you as
>>> http://paste.openstack.org/show/543105/ , it should work for you
> [Hongbin Lu] It looks the fundamental difference between the proposed patch (https://review.openstack.org/#/c/343060/8/magnum/api/controllers/v1/bay.py) and the snippet (http://paste.openstack.org/show/543105/) is the usage of a decorator "api_version". The proposed patch implemented the decorator and used it to select the right version while the snippet selected the version inline. I lean to the decorator implementation because it looks clean and seems to effectively reduce duplicated codes.
>
>>>      3. we don't have too may requirements to bump our microversion (I
>>> know you want to use it in bay-creation async), so we don't want
>> bring
>>> much code here then we need to maintain it later.
> [Hongbin Lu] It is hard to forecast how frequent we need to bump the microversion. If we will bump the version frequently, the decorator implementation looks like the right approach. If not, implementing a decorator looks like an over-killed but I doubt if it will incur significant maintenance burden.
>
>>>      4. the community are discussing to using Semantic
>>> Versioning(X.Y.Z) [1] instead of microversion X.Y
>> [1]http://semver.org/
>>>     If you have any questions , please discuss it in mailing list or
>>> weekly meeting.
>>>     Eli.
>>>
>>>
>>>
>>> Jaycen Grant
>>> OSIC
>>>
>>>
>>>
>>>
>>> [1] http://specs.openstack.org/openstack/api-
>>>
>> wg/guidelines/microversion_specification.html?highlight=microversionin
>>> g
>>>
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-- 
Best Regards,
Eli Qiao (乔立勇), Intel OTC.


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