[Pulp-dev] Pulp 3 REST API Challenges

Wed Apr 18 07:07:47 UTC 2018

I believe option 1 is a better fit as I think a new repository version
is a side-effect of a (plug-in specific) action on a repository.

Cheers,
milan

On Mon, Apr 16, 2018 at 10:31 PM, Dennis Kliban <dkliban at redhat.com> wrote:
> On Fri, Apr 13, 2018 at 3:55 PM, Jeff Ortel <jortel at redhat.com> wrote:
>>
>>
>>
>> On 04/12/2018 04:49 PM, Dennis Kliban wrote:
>>
>> On Thu, Apr 12, 2018 at 2:49 PM, Jeff Ortel <jortel at redhat.com> wrote:
>>>
>>>
>>>
>>> On 04/11/2018 01:13 PM, Dennis Kliban wrote:
>>>
>>> On Tue, Apr 10, 2018 at 6:44 PM, Jeff Ortel <jortel at redhat.com> wrote:
>>>>
>>>>
>>>>
>>>> On 04/10/2018 04:15 PM, Dennis Kliban wrote:
>>>>
>>>> On Tue, Apr 10, 2018 at 2:04 PM, Brian Bouterse <bbouters at redhat.com>
>>>> wrote:
>>>>>
>>>>> These are good problem statements. I didn't understand all of the
>>>>> aspects of it, so I put some inline questions.
>>>>>
>>>>> My overall question is: are these related problems? To share my answer
>>>>> to this, I believe the first two problems are related and the third is
>>>>> separate. The classic divide and conquor approach we could use here is to
>>>>> confirm that the problems are unrelated and focus on resolving one of them
>>>>> first.
>>>>>
>>>>
>>>> I don't think all 3 are related problems. The motivation for grouping
>>>> all together is that a subset of the action endpoints from problem 1 are
>>>> used to create repository versions and Problem 3 is a problem with the
>>>> repository version creation API.
>>>>
>>>>>
>>>>>
>>>>> On Mon, Apr 9, 2018 at 3:18 PM, Austin Macdonald <austin at redhat.com>
>>>>> wrote:
>>>>>>
>>>>>> Folks,
>>>>>>
>>>>>> Austin, Dennis, and Milan have identified the following issues with
>>>>>> current Pulp3 REST API design:
>>>>>>
>>>>>> Action endpoints are problematic.
>>>>>>
>>>>>> Example POST@/importers/<plugin>/sync/
>>>>>> They are non-RESTful and would make client code tightly coupled with
>>>>>> the server code.
>>>>>> These endpoints are inconsistent with the other parts of the REST API.
>>>>>
>>>>> Is self-consistency really a goal? I think it's a placeholder for
>>>>> consistency for REST since the "rest" of the API is RESTful. After reading
>>>>> parts of Roy Fielding's writeup of the definition of REST I believe "action
>>>>> endpoints are not RESTful" to be a true statement. Maybe "Action endpoints
>>>>> are problematic" should be replaced with "Action endpoints are not RESTful"
>>>>> perhaps and have the self-consistency bullet removed?
>>>>
>>>>
>>>> +1 to "Action endpoints are not RESTful"
>>>> +1 to removing the self-consistency language
>>>>
>>>>>>
>>>>>> DRF is not being used as intended for action endpoints so we have to
>>>>>> implement extra code. (against the grain)
>>>>>
>>>>> I don't know much about this. Where is the extra code?
>>>>>
>>>>>>
>>>>>> We don't have a convention for where plug-in-specific, custom
>>>>>> repository version creation endpoints.
>>>>>>
>>>>>> example POST@/api/v3/<where?>/docker/add/
>>>>>> needs to be discoverable through the schema
>>>>>
>>>>> What does discoverable via the schema ^ mean? Aren't all urls listed in
>>>>> the schema?
>>>>>
>>>>> I think of ^ problem somewhat differently. Yes all urls need to be
>>>>> discoverable (a REST property), but isn't it more of an issue that the urls
>>>>> which produce repo versions can't be identified distinctly from any other
>>>>> plugin-contributed url? To paraphrase this perspective: making a repo
>>>>> version is strewn about throughout the API in random places which is a bad
>>>>> user experience. Is that what is motivation url discovery?
>>>>>
>>>>
>>>>
>>>> Yes. I envision a CLI that can discover new plugin
>>>> repository-version-creating functionality without having to install new
>>>> client packages. Allowing plugin writers to add endpoints in arbitrary
>>>> places for creating repository versions will make it impossible for the
>>>> client to know what all the possible ways of creating a repository version
>>>> are.
>>>>
>>>>>>
>>>>>> For direct repository version creation, plugins are not involved.
>>>>>>
>>>>>> validation correctness problem: https://pulp.plan.io/issues/3541
>>>>>> example: POST@/api/v3/repositories/<repository_id>/versions/
>>>>>
>>>>> I agree with this problem statement. In terms of scope it affects some
>>>>> plugin writers but not all.
>>>>
>>>>
>>>> I think it affects all plugin writers. Even the File plugin needs to
>>>> provide some validation when creating a repository version. Right now you
>>>> can add a FileContent with the same relative path as another FileContent in
>>>> the repository version. This should not be possible because it's not a valid
>>>> combination of FileContent units in the same repository version.
>>>>
>>>>
>>>> Not necessarily.  Two files with the same relative path will have
>>>> different digest (different content).  The assumption that they both cannot
>>>> be in the same repository makes assumptions about how the repository is used
>>>> which I don't think is a good idea.  Image two different versions of
>>>> abc.iso.
>>>>
>>>
>>> Why is it bad to assume that a repository version is going to be
>>> published? What are the other ways to use a repository version?
>>>
>>>
>>> The repository may not be publish and/or may not be published by the
>>> FilePublisher in the file plugin project.  A user may want to sync and store
>>> many version of an iso in the repository and then selectively add a specific
>>> version to another repository for promotion work flows.  Also, the user
>>> could use another (custom) publisher that deals differently with multiple
>>> files with the same path in the repository.  The FilePublisher currently
>>> publishes the newest.  My point being, we, really cannot assume how the
>>> repository will be used or which publisher may publish it.
>>>
>>
>> The problem was initially stated as "For direct repository version
>> creation, plugins are not involved". It sounds like you disagree that this
>> is a problem.
>>
>>
>> Yes.  Definitely, agreed.
>>
>> Can you confirm this by telling us if plugins should be able to provide
>> validation for this API provided by core?
>>
>>
>> Plugins participating in core endpoints is different, broader discussion.
>>
>> The following is not aimed at you dkliban :)
>>
>> We need to decide if we want to return to the pulp2 pattern whereby the
>> core delegates behavior to plugins via the plugin API.  Or, continue down
>> the pulp3 path whereby operations involving plugins are contributed to the
>> API by each plugin (not making a value judgment). Also, I value consistency
>> in APIs and don't think these approaches should be mixed (with the exception
>> of content related live-API).  Consistency in APIs reflect both a
>> thoughtful, mature design and provides a better user experience. I'm sure
>> everyone has cursed APIs that did things every-which-way. I don't think
>> there is any difference between creating a repository version via sync or
>> creating a version with a list of content to add/remove.  And to a lesser
>> degree publishing.  We should either POST to the /publications/ endpoint for
>> creating a publication (core API), or users should POST to the plugin
>> contributed endpoint (as currently) for publishing.
>>
>> Seems to me, there are 2 high-level choices:
>>
>> 1.  Core endpoints do not delegate/redirect to plugins.
>>      - POST to /RepositoryVersion/ is removed.
>>      - POST to /Publications/  (stays gone)
>>      - Plugins provide endpoints for sync and other to create new
>> repository versions.
>>      - Plugins provide endpoints for creating Publications (publishing).
>>
>> 2. Core delegates behavior to plugins for those endpoints requiring plugin
>> participation.
>>     - POST to /RepositoryVersion/ is the only way to create a repository
>> version.
>>     - POST to /Publications/  is the only way to create a Publication
>> (publish).
>>     - The POST parameters or body includes enough information so that core
>> can select a plugin.
>>     - Either the entire POST is passed along to the plugin, or the plugin
>> implements an API that's used by
>>       core for pre-defined participation.
>>
>
> I prefer option 2 because it makes obvious for the user which 2 APIs to use
> when creating repository versions and publications.
>
>>
>> There have been proposals on how both #1 and #2 can be achieved. 'm
>> wondering if we can even agree on one of these two approaches.
>>
>>
>>> A File repository version cannot be properly published if it contains 2
>>> FileContent units that both have the same relative path. The publisher has
>>> to decide which FileContent to publish at the relative path. That decision
>>> cannot be made intelligently by the publisher. The decision on which content
>>> unit to include in the repository version rests with the user that is
>>> creating the repository version. When a user tries to create a repository
>>> version with a FileContent that has the same relative path as another
>>> FileContent that was added previously, Pulp needs to inform the user that
>>> there is a conflict (and not create the repositiory version). This
>>> validation can only be provided by the File plugin.
>>>
>>>>
>>>>
>>>>>
>>>>>
>>>>>>
>>>>>> We would like to get feedback on these issues being sound and worth
>>>>>> resolving before we resume particular solution discussion[1].
>>>>>>
>>>>>> Thanks,
>>>>>> Austin, Dennis, and Milan
>>>>>>
>>>>>> [1] https://www.redhat.com/archives/pulp-dev/2018-March/msg00066.html
>>>>>>
>>>>>>
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>>>>>>
>>>>>
>>>>>
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>>>>
>>>>
>>>>
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