[Pulp-dev] [pulp 3] proposed change to publishing REST api
Brian Bouterse
bbouters at redhat.com
Wed Nov 1 14:16:28 UTC 2017
Thanks for the response. Let's not move forward until we have more
agreement in this area. I've written some responses inline.
On Wed, Nov 1, 2017 at 9:05 AM, Jeff Ortel <jortel at redhat.com> wrote:
> I'm not yet convinced about the proposed URL change for publishing. Can
> you help me understand why a POST to
> the publications collection is more appropriate than the a POST to a
> publisher?
>
I believe the thinking is: REST suggests that POSTing to a resource is
expected to create a new resource of that type. So assume a users knows
REST and they know they want to get a Publication created in Pulp, they
know exactly how to do that just by knowing REST. In the case of a POST to
a publisher url with a special 'publish' keyword on the end of it (the
controller endpoint), they only way a user could know to do that is by
reading our docs. Both approaches would work, but I believe the former is
more aligned with REST which means users can do more without having to read
Pulp docs.
>
> A POST to the publications/ collection means the POST body should define
> the publication to be created.
> Right? What about options that need to be passed to the publisher?
>
Yes, if we look at the fields of the publisher (link below), there are only
two fields: 'created' and 'publisher'. Since 'created' is set on the server
automatically, the user would specify only the href to the publisher in the
POST body. For the MVP, we don't accept one-time options, and all other
options are configured on the publisher which is a different url call from
both the publish controller and the publication resource. So for the MVP
this approach would work well. The future case also is better with this
approach (I think). When we do introduce one-time options, where will we
store them? We will probably be store them on the publication too, and that
makes sense, because we can't store N, one-time publish options on 1
publisher instance, but we can store N, one-time publish options on N
publications.
https://github.com/pulp/pulp/blob/15857fb0831c0998219a32e8d6ba52abdba20888/platform/pulpcore/app/models/publication.py#L6
>
> On 10/31/2017 03:13 PM, Brian Bouterse wrote:
> > @dkliban, I'm +1 on that.
> >
> > @all, Please jump in if this is not the best direction for us to go.
> >
> > On Tue, Oct 31, 2017 at 3:55 PM, Dennis Kliban <dkliban at redhat.com
> <mailto:dkliban at redhat.com>> wrote:
> >
> > On Tue, Oct 31, 2017 at 3:52 PM, Brian Bouterse <bbouters at redhat.com
> <mailto:bbouters at redhat.com>> wrote:
> >
> > Would that return the 202 w/ a link to the task because the
> publication hasn't been created yet? Then
> > using the created_resources they can see what was created, and
> in the event of failure the task fails
> > and there are no created_resources.
> >
> > @dkliban is ^ the idea?
> >
> >
> > Yes, the response would the same as it for the /publish URL right
> now. This is just a change in the URL
> > that is used to make the request.
> >
> >
> >
> > On Tue, Oct 31, 2017 at 3:48 PM, Dennis Kliban <
> dkliban at redhat.com <mailto:dkliban at redhat.com>> wrote:
> >
> >
> >
> > On Tue, Oct 31, 2017 at 3:40 PM, Brian Bouterse <
> bbouters at redhat.com <mailto:bbouters at redhat.com>>
> > wrote:
> >
> > +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?
> >
> >
> > This API call creates a publication resource. A POST to
> publishers/<id>/publications/ seems most
> > appropriate for creating new publication resources.
> >
> > 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
> > <mailto: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
> > <mailto:dkliban at redhat.com>> wrote:
> >
> > On Wed, Oct 25, 2017 at 11:24 AM, David Davis <
> daviddavis at redhat.com
> > <mailto: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
> > <mailto:bbouters at redhat.com>> wrote:
> >
> >
> >
> > On Tue, Oct 24, 2017 at 10:00 PM,
> Michael Hrivnak <mhrivnak at redhat.com
> > <mailto:mhrivnak at redhat.com>> wrote:
> >
> >
> >
> > On Tue, Oct 24, 2017 at 2:11 PM,
> Brian Bouterse <bbouters at redhat.com
> > <mailto: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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> >
> >
> >
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