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Re: [Pulp-dev] Plugin Writer's Coding Workshop Feedback

Sorry just getting back to this now... Thanks for the redmine tickets, and also for the questions. I wrote some on the tickets, including the desire for the sqlite database on the sqlite ticket here: https://pulp.plan.io/issues/3359

re: the confusion about the class/function names in pulp_file. The confusion I think comes from someone who isn't familiar with the Pulp3 plugin API and mistakes the arbitrary functions and class names as being significant and required. It's side-by-side other objects they have to provide so I can understand this confusion.

re: the pulp_file and changesets, the thing I've become aware of is that we don't have simple examples for what plugin code should do and the changesets as our reference example makes explaining these things more challenging. Maybe we need another importer implementation, but we tried that with pulp_example and we couldn't maintain both. Out of date examples are even worse, and at the workshop it created epic confusion as people mimicked outdated code only to find their implementations broken from the start.

I thought about pulp_file very differently, so I'm glad you wrote it out. I think of pulp_file as a reference plugin that clearly demonstrates how to use the Plugin API and all the objects in it. It's the thing I want to open when we are giving a plugin writer an example to talk about Artifacts, ContentUnits, Downloading, uniqueness checking, etc. One of the takeaways for me is that we should delete pulp_example. It's out of date and we shouldn't try to fix it.

It would be great to have some more input from others on these things. Thanks for all the discussion.

On Tue, Feb 13, 2018 at 10:50 AM, Jeff Ortel <jortel redhat com> wrote:
Thanks for providing this feedback, Brian.!  Good stuff.

On 02/12/2018 03:57 PM, Brian Bouterse wrote:
At the Foreman Construction day [0] last Wednesday, we had our first code focused plugin writer's workshop. About 6 people were actively engaged as we talked through the plugin API, example code, and then tried to install Pulp3. All of this happened over about 4-5 hours. In contrast to the devconf workshop which was planning focused, this was a "let's look at and write some code together" workshop. Two attendees came to both, and they got all the way to calling their own sync code.

We got a lot of feedback, which I will try to group into some areas. (my feedback in parens)

[installation issues]
- the pypi install commands are missing the migrations and they produce broken installations
- the vagrantcloud boxes couldn't have a plugin installed on them :(
- the dev environments worked great but we didn't recommend them until we realized all of these other methods were broken
- we assume the user 'pulp' in a lot of places, e.g. systemd file, ansible, etc
- assumptions about Fedora both in ansible, but also the copy/paste commands
- some users who copied and pasted commands didn't realize they weren't for their OS

[desire for simpler things]
- there is a strong desire to use sqlite as the default db not postgresql

Very interesting.  Can you elaborate about why?

- desire to not install a message bus. (I think this is unavoidable)

[need examples]
- pulp_file is our example, but it's laid out into different functions and classes. People were confused by this because they thought the classes and function names are meaningful when they aren't. For example we were asked "what is a synchronizer" https://github.com/pulp/pulp_file/blob/master/pulp_file/app/tasks.py#L139

The Synchronizer used to be the FileImporter and got renamed as part of early mitigation of the "circular import" problem.  I plan to do some final refactoring as soon as the plugin API stabilizes (really soon).  I suspect the Synchronizer class (at least the name), will go away.  That said, I'm a little puzzled as to what led to actual "confusion" about a class named Synchronizer that was used to synchronize a repository.  You also mentioned that some of the function names where somehow confusing - can you name them and why they were confusing?

- pulp_file doesn't provide a good example because changesets do everything for you. (The main pulp_file should be a simple, direct example of the objects they have to save).

True, but It does provides a good example of how to use the ChangeSet.

- people found pulp_example via github and thought "oh here is what I needed to find!" only to base their code on outdated code (we need to delete pulp_example)
- a database picture would be helpful to show off the data layer objects, foreign keys, and attributes.

Yes!  We really need to publish an ER diagram.  I'm overdue on an action item to produce one.

[specific things]
- 'id' on the inherited content unit conflicted with a content unit which also uses 'id'.
- qpid vs rabbitmq defaults confusion. The settings.yaml says we default to qpid so they installed qpid, but really in settings.py it's rabbitmq. (this is a 1 line fix)

In terms of the installation challenges, we should consider consolidating onto a single installation method of pip with virtualenv. Of all the methods we offer [1] that is the one everyone could use and no one minded. We could remove the other options from the install page so that for for now (pre-GA) everyone is doing the same, simple thing. I think we should consolidate our effort and not focus on end-user installations as the main thing right now.**

I also think we should do these things:

* switch pulp to use sqlite3 by default. An ansible installer can both install postgres and configure it, later.
* rewrite pulp_file to be a really really simple example

The file-plugin is already a "really really simple example".  Rewriting it not using the ChangeSet will significantly increase code line count and complexity.  As you know, the file-plugin supports managing FileContent like .img and .iso files.  The primary goal of the pulp-file project is to support real use cases.  Because it's the only plugin, it has taken on a secondary goal of being an example.  I'm opposed to increasing complexity in support of the secondary "example" goal at the expense of its primary goal. 

The file-plugin currently provides a good example of how to use the ChangeSet.  I have no doubt that plugin writers want additional examples but I think that if we intend to continue to rely on "real" plugins as natural examples, we should identify a plugin on the roadmap that has made the design choice to be implemented without the ChangeSet and prioritize it.  Another choice could be to refactor the example plugin to support a broader range of examples and continue to maintain it.

* delete pulp_example

Please send ideas, questions, or any kind of feedback.

[0]: http://cfgmgmtcamp.eu/fringe.html#foreman
[1]: https://docs.pulpproject.org/en/3.0/nightly/installation/index.html

** I still see Ansible as the right cross-distro installer as we approach the GA date. @ichimonji10 I  am still +1 on your proposal, I think we just need to consolidate both dev and testing effort for now. This is similar to the approach for the migration tool which we know is really important but we aren't starting yet.


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