[Pulp-dev] Consider moving distribution to top level resource.

[Jeff Ortel]

During a discussion with Austin to resolve a problem implementing #3033, an interested question was raised -
"Why do Distributions needs to be owned by Publishers?"  This question came up when considering a solution to
a DRF difficulty related to both Publications and Distributions being nested under publisher/ AND related to
each other.  The idea being considered was to move Distributions to a top level resource.  Here are the benefits:

1. Resolves current DRF nesting issue w/ #3033.  (This is minor).
2. A distribution could be updated to reference any publication.  This is more flexible.
3. Since Distribution.base_path is unique across all repositories/publishers, it might be more intuitive to be
a top level resource?

Currently, the Distribution.publisher_id represents a parent-child relationship the mainly exists to support
automatic distribution.  When the publisher creates a new publication, it is automatically associated to any
of the publisher's distributions marked as auto_updated=True.

There are two challenges to moving the Distribution to a top-level resources.

1. The distribution name is currently unique by (publisher_id, name).
2. This would break automatic distribution as currently implemented.

Here are a few options to resolving these challenges:

1. The name could be unique across all distributions.  This seems reasonable.
2. Redesign automatic distribution.  (see proposal below).
3. Reconsider automatic distribution.

---

Proposal to redesign automatic distribution.

The use case for automatic distribution is similar to automatic publishing.  The user has updated a
repository; has published it; and now wants to consume content.  This could be done by making 3 API calls: 1
sync; 2 publish; 3 update-a-distribution.  But, based on pulp2, users want to do this with 1 API call.

So, here is the proposal.

1. Move distributions to the top level resource (no longer owned by a publisher).
2. Remove Distribution.publisher_id and Distribution.auto_updated.
3. Add (optional) Publisher.distribution_id.  When set, the referenced distribution will be updated with newly
created publications.


Publisher <---* Publication
   |                ^ (0,1)
   |                |
   |                |
   v (0,1)          |
Distribution --------

---

I'm not convinced about all this but think we should consider.

Thoughts?


https://pulp.plan.io/issues/3033

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