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How Plugins Work

Plugin Django Application

Like the Pulp Core itself, all Pulp Plugins begin as Django Applications, started like any other with pulpcore-manager startapp <your_plugin>. However, instead of subclassing Django's django.apps.AppConfig as seen in the Django documentation, Pulp Plugins identify themselves as plugins to pulpcore by subclassing {class}pulpcore.plugin.PulpPluginAppConfig.

{class}pulpcore.plugin.PulpPluginAppConfig also provides the application autoloading behaviors, such as automatic registration of viewsets with the API router, which adds plugin endpoints.

The {class}pulpcore.plugin.PulpPluginAppConfig subclass for any plugin must set a few required attributes:

  • name attribute defines the importable dotted Python location of the plugin application (the Python namespace that contains at least models and viewsets).
  • label attribute to something that unambiguously labels the plugin in a clear way for users. See how it is done in the pulp_file plugin.
  • version attribute to the string representing the version.

pulpcore.plugin Entry Point

The Pulp Core discovers available plugins by inspecting the pulpcore.plugin entry point.

Once a plugin has defined its {class}pulpcore.plugin.PulpPluginAppConfig subclass, it should add a pointer to that subclass using the Django default_app_config convention, e.g. default_app_config = somewhere in the module that contains your Django application. The Pulp Core can then be told to use this value to discover your plugin, by pointing the pulpcore.plugin entry point at it. If, for example, we set default_app_config in pulp_myplugin/, the entry_points would look like this:

    'pulpcore.plugin': [
        'pulp_myplugin = pulp_myplugin:default_app_config',

If you do not wish to use Django's default_app_config convention, the name given to the pulpcore.plugin entry point must be an importable identifier with a string value containing the importable dotted path to your plugin's application config class, just as default_app_config does.

Check out pulp_file plugin: default_app_config and example.

Model, Serializer, Viewset Discovery

The structure of plugins should, where possible, mimic the layout of the Pulp Core Plugin API. For example, model classes should be based on platform classes imported from {mod}pulpcore.plugin.models and be defined in the models module or directory of a plugin app. ViewSets should be imported from {mod}pulpcore.plugin.viewsets, and be defined in the viewsets module of a plugin app, and so on.

This matching of module names is required for the Pulp Core to be able to auto-discover plugin components, particularly for both models and viewsets.

Take a look at the structure of the pulp_file plugin.

Serializer and OpenAPI schema

Serializers are converted to OpenAPI objects through drf-spectacular. It inspects all serializer fields to describe them in the OpenAPI schema. Due to the DRF issue it is preferable to use CharField instead of URLField. Otherwise The REST API hosted at /pulp/api/v3/ may hide some paths.