[Pulp-dev] [pulp 3] proposed change to publishing REST api

Tue Oct 31 19:40:13 UTC 2017

+1 to updating #3033 to have a created_resources attribute which would be a
list of GenericForeignKeys. It also needs docs, but I'm not entirely sure
where.

If we're going to introduce the above attribute, I think having the
controller endpoint as-is would be the most usable. @dkliban do you see
value in changing the URL structure if the created_resources attribute is
introduced?

I can help review/groom these if that is helpful.

-Brian

On Tue, Oct 31, 2017 at 1:39 PM, David Davis <daviddavis at redhat.com> wrote:

> Personally I am not opposed to the url endpoint you suggest.
>
> It also seems like there is some consensus around adding a ‘created
> resources’ relationship to Task or at least prototyping that out to see
> what it would look like.
>
> If no one disagrees, should I update issue #3033 with those two items?
>
>
> David
>
> On Wed, Oct 25, 2017 at 1:23 PM, Dennis Kliban <dkliban at redhat.com> wrote:
>
>> On Wed, Oct 25, 2017 at 11:24 AM, David Davis <daviddavis at redhat.com>
>> wrote:
>>
>>> I don’t know that the ambiguity around whether a task has a publication
>>> or not is a big deal. If I call the publication endpoint, I’d expect a
>>> publication task which either has 1 publication or 0 (if the publication
>>> failed) attached to it.
>>>
>>> In terms of ambiguity, I see a worse problem around adding a task_id
>>> field to publications. As a user, I don’t know if a publication failed or
>>> not when I get back a publication object. Instead, I have to look up the
>>> task to see if it is a real (or successful) publication. Moreover, since we
>>> allow users to remove/clean up tasks, that task may not even exist anymore.
>>>
>>>
>> I agree that the ephemeral nature of tasks makes the originally proposed
>> solution non-deterministic. I am open to associating 'resources created'
>> with a task instead.
>>
>> However, I still think there is value in changing the rest API endpoint
>> for starting a publish task to POST /api/v3/repositories/<repo-id>
>> /publishers/<type>/<name>/publications/. However, I will start a
>> separate thread for that discussion.
>>
>>  - Dennis
>>
>>
>>>
>>> David
>>>
>>> On Wed, Oct 25, 2017 at 11:03 AM, Brian Bouterse <bbouters at redhat.com>
>>> wrote:
>>>
>>>>
>>>>
>>>> On Tue, Oct 24, 2017 at 10:00 PM, Michael Hrivnak <mhrivnak at redhat.com>
>>>> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Tue, Oct 24, 2017 at 2:11 PM, Brian Bouterse <bbouters at redhat.com>
>>>>> wrote:
>>>>>
>>>>>> Thanks everyone for all the discussion! I'll try to recap the problem
>>>>>> and some of the solutions I've heard. I'll also share some of my
>>>>>> perspective on them too.
>>>>>>
>>>>>> What problem are we solving?
>>>>>> When a user calls "publish" (the action API endpoint) they get a 202
>>>>>> w/ a link to the task. That task will produce a publication. How can the
>>>>>> user find the publication that was produced by the task? How can the user
>>>>>> be sure the publication is fully complete?
>>>>>>
>>>>>>
>>>>>> What are our options?
>>>>>> 1) Start linking to created objects from task status. I believe its
>>>>>> been clearly stated about why we can't do this. If it's not clear, or if
>>>>>> there are other things we should consider, let's talk about it.
>>>>>> Acknowledging or establishing agreement on this is crucial because a change
>>>>>> like this would bring back a lot of the user pain from pulp2. I believe the
>>>>>> HAL suggestion falls into this area.
>>>>>>
>>>>>
>>>>> I may have missed something, but I do not think this is clear. I know
>>>>> that Pulp 2's API included a lot of unstructured data, but that is not at
>>>>> all what I'm suggesting here.
>>>>>
>>>>> It is standard and recommended practice for REST API responses to
>>>>> include links to resources along with information about what type of
>>>>> resource each link references. We could include a reference to the created
>>>>> resource and an identifier for what type of resource it is, and that would
>>>>> be well within the bounds of good REST API design. HAL is just one of
>>>>> several ways to accomplish that, and I'm not pitching any particular
>>>>> solution there. In any case, I'm not sure what the problem would be with
>>>>> this approach.
>>>>>
>>>>
>>>> I agree it is a standard practice for a resource to include links to
>>>> other resources, but the proposal is to include "generic" links is
>>>> different and creates a different user experience. I believe referencing
>>>> the task from the publication will be easier for users and clients. When a
>>>> user looks up a publication, they will always know they'll get between 0
>>>> and 1 links to a task. You can use that to check the state of the
>>>> publication. If we link to "generic" resources (like a publication) from a
>>>> task, then if I ask a user "do you expect task
>>>> ede3af3e-d5cf-4e18-8c57-69ac4d4e4de6 to contain a link to a
>>>> publication or not?" you can't know until you query it. I think that
>>>> ambiguity was a pain point in Pulp2. I don't totally reject this solution,
>>>> but this is an undesirable property (I think).
>>>>
>>>>
>>>>>
>>>>>>
>>>>>> 2) Have the user find the publication via query that sorts on time
>>>>>> and filters only for a specific publisher. This could be fragile because
>>>>>> with a multi-user system and no hard references between publications and
>>>>>> tasks, answering the question "which is the publication for me" is hard
>>>>>> because another user could have submitted a publish too. While not totally
>>>>>> perfect, this could work.
>>>>>>
>>>>>
>>>>> In theory if a user queried for a publication from a specific
>>>>> publisher that was created between the start and end times of the task,
>>>>> that should unambiguously identify the correct publication. But depending
>>>>> on timestamps is not a particularly robust nor confidence-inspiring way to
>>>>> reference a resource.
>>>>>
>>>> Agreed and Agreed
>>>>
>>>>
>>>>>
>>>>>>
>>>>>> 3) Have the user create a publication directly like any other REST
>>>>>> resource, and help the user understand the state of that resource over
>>>>>> time. I believe the proposal at the start of this thread is recommending
>>>>>> this solution. I'm also +1 on this solution.
>>>>>>
>>>>>
>>>>> I think the problem with this is that a user cannot create a
>>>>> publication. A user can only ask a plugin to create a publication. Until
>>>>> the plugin creates the publication, there is no publication.
>>>>>
>>>>
>>>> Note a publication is an object, but really we mean a publication and
>>>> it's related PublishedArtifact, PublishedMetadat, etc objects. It would be
>>>> straightforward for a user to create a publication using the viewset and
>>>> have the task associated with it call the publisher to build out the
>>>> associated PublishedArtifact, PublishedContent, PublishedMetadata, etc. We
>>>> should explore if this is good or not, but it is possible.
>>>>
>>>> As an aside, this is related to a problem everyone should be aware of:
>>>> the existence of a publication does not guarantee that publication is
>>>> finished publishing. Even with option 1, where the task creates the
>>>> publisher and links to it in the task status, while the publisher is
>>>> running it must save the Publication so that the PublishedArtifact, etc can
>>>> link to it. So for any given publication, in order to know if it's "fully
>>>> finished and consistent" you must be able to check the status of the
>>>> associated task that produced it.
>>>>
>>>>
>>>>>
>>>>>> As an aside, I don't think considering versioned repos as a possible
>>>>>> solution is helping us with this problem. The scope of the current problem
>>>>>> is relatively small and the scope of planning for versioned repos is large.
>>>>>>
>>>>>>
>>>>> Versioned repos is a potential solution. In that scenario, a user
>>>>> would request publication of a specific repo version (perhaps defaulting to
>>>>> the latest), the publication would be linked to that version, and that is
>>>>> an easy mechanism for the user to find the publication they want.
>>>>> Ultimately the user is interested in working with a specific content set
>>>>> anyway. They get a repo to a state where it has the content they want, and
>>>>> then they publish that content set. No matter what we do with publications,
>>>>> users will think of them in terms of related content sets. A repo version
>>>>> is that immutable content set they can work with confidently.
>>>>>
>>>>
>>>> It's neat to me that that versions are snapshots of content and
>>>> publications are snapshots of content. Publications already create much of
>>>> the value propostion of versioned repos with publications. They allow you
>>>> to work with specific content sets like you describe. Also they allow for
>>>> rollback. So that is all great for our users. For this thread, I want to
>>>> bring the conversation back to where it started, solving a small problem
>>>> about linking two resources that already exist.
>>>>
>>>>
>>>>> It helps the rollback scenario a lot as well. Versioning repos allows
>>>>> a user to see what the differences are between two content sets, and thus
>>>>> two different publications, which informs them about when and how far back
>>>>> they should roll back a distribution.
>>>>>
>>>>
>>>>> - user discovers a horrible flaw in a piece of content
>>>>> - user queries for which version of the repo introduced that piece of
>>>>> content
>>>>> - user updates the distribution to serve the publication that came
>>>>> before the one which introduced the piece of content, optionally
>>>>> re-publishing that version in case its publication was deleted or had never
>>>>> been made in the first place.
>>>>>
>>>>> --
>>>>>
>>>>> Michael Hrivnak
>>>>>
>>>>> Principal Software Engineer, RHCE
>>>>>
>>>>> Red Hat
>>>>>
>>>>
>>>>
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>>>> Pulp-dev at redhat.com
>>>> https://www.redhat.com/mailman/listinfo/pulp-dev
>>>>
>>>>
>>>
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>>>
>>>
>>
>
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