Plugin Concepts

Like the Pulp Core itself, all Pulp Plugins are Django Applications, and could be created like any other Django app with pulpcore-manager startapp <your_plugin>. However, instead of writing all of the boilerplate yourself, it is recommmended that you start your plugin by utilizing the Plugin Template. This guide will assume that you have used the plugin_template, but if you are interested in the details of what it provides you, please see Plugin Django Application for more information for how plugins are “discovered” and connected to the pulpcore Django app. Additional information is given as inline comments in the template.

Plugin API Usage

Plugin Applications interact with pulpcore with two high level interfaces, subclassing and adding tasks.

Subclassing

Pulp Core and each plugin utilize Django and the Django Rest Framework. Each plugin provides Models, Serializers, and Viewsets. For each object that a plugin writer needs to make, the pulpcore.plugin API provides base classes. These base classes handle most of the boilerplate code, resulting in CRUD for each object out of the box.

• Models
  • Adding Model Fields
  • Uniqueness
  • ForeignKey Gotchas
• Serializers
  • Adding Fields
• Viewsets
  • Endpoint Namespacing
  • Detail Routes (Extra Endpoints)

Tasks

Any action that can run for a long time should be an asynchronous task. Plugin writers do not need to understand the internals of the pulpcore tasking system, workers automatically execute tasks from RQ, including tasks deployed by plugins.

Reservations

The tasking system adds a concept called reservations which ensures that actions that act on the same resources are not run at the same time. To ensure data correctness, any action that alters the content of a repository (thus creating a new version) must be run asynchronously, locking on the repository and any other models which cannot change during the action. For example, sync tasks must be asynchronous and lock on the repository and the remote. Publish should lock on the repository version being published as well as the publisher.

Deploying Tasks

Tasks are deployed from Views or Viewsets, please see Kick off Tasks.

• Adding and Removing Content
  • Repository Versions
  • Synchronizing
• Publish
• Export Task

Sync Pipeline

• Synchronizing Repositories with the async-Pipeline
  • On-demand synchronizing
  • Multiple level discovery

Content Protection

Users can configure a ContentGuard to protect a Distribution on their own, but some plugins want to offer built-in content protection features. For example pulp_container may only want a user to download container images they have rights to based on some permissions system pulp_container could provide.

For more information see the ContentGuard Usage by Plugin Writers documentation.

Plugin Settings

Plugins can define settings by creating a <your plugin>.app.settings module containing settings as you would define in the Django Settings File itself. pulpcore ships the actual settings.py file so settings cannot be added directly as with most Django deployments. Instead as each plugin is loaded, pulpcore looks for the <your plugin>.app.settings module and uses dynaconf to overlay the settings on top of pulpcore’s settings and user provided settings.

Settings are parsed in the following order with later settings overwriting earlier ones:

1. Settings from /etc/pulp/settings.py.

2. Settings from pulpcore.app.settings (the pulpcore provided settings defaults).

3. Plugin settings from <your plugin>.app.settings.

In some cases a setting should not overwrite an existing setting, but instead add to it. For example, consider adding a custom log handler or logger to the LOGGING settings. You don’t want to fully overwrite it, but instead add or overwrite only a sub-portion. dynaconf provides the dynaconf_merge feature which is for merging settings instead of overwriting them. For example, pulp_ansible makes use of this here.

Custom API URL Routes

The typical plugin viewsets are all suburls under /pulp/api/v3/, but some content types require additional urls outside of this area. For example pulp_ansible provides the Galaxy API at /pulp_ansible/galaxy/.

Place a urls.py that defines a urlpatterns at the root of your Python package, and the pulpcore plugin loading code will append those urls to the url root. This allows your urls.py to be a typical Django file. For example pulp_ansible uses a urls.py defined here

Custom Content App Routes

The Content App may also require custom routes, for example pulp_container defines some. Read more about how to customize the content app with custom routes.

Configuring Reverse Proxy with Custom URLs

When a plugin requires either Pulp API or Pulp Content App custom urls, the reverse proxy, i.e. either Nginx or Apache, need to receive extra configuration snippets to know which service to route the custom URLs to.

A best practice is to document clearly the custom URL requirements your plugin needs. Although the installer can automatically install plugin snippets, other environments, e.g. k8s or docker or docker containers may still need to configure them manually. Having clear docs is a minimum.

You can ship snippets of configuration and have the installer install them as follows. You’ll need to create a python package named webserver_snippets directory inside your app, e.g. pulp_ansible.app.webserver_snippets. Like all Python packages it will have an __init__.py. You’ll also create an apache.conf and an nginx.conf, and the installer will symlink to the correct one depending on which reverse proxy is installed.

Create the Nginx and Apache snippets as follow:

$ tree webserver_snippets/
webserver_snippets/
├── __init__.py
├── apache.conf
└── nginx.conf

0 directories, 3 files

The Nginx config provides definitions for the location of the Pulp Content App and the Pulp API as pulp-api and pulp-content respectively. To route the url /pulp_ansible/galaxy/ to the Pulp API you could use this definition in a snippet like:

location /pulp_ansible/galaxy/ {
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_set_header Host $http_host;
    # we don't want nginx trying to do something clever with
    # redirects, we set the Host: header above already.
    proxy_redirect off;
    proxy_pass http://pulp-api;
}

The Apache config provides variables containing the location of the Pulp Content App and the Pulp API as pulp-api and pulp-content respectively. Below is an equivalent snippet to the one above, only for Apache:

ProxyPass /pulp_ansible/galaxy http://${pulp-api}/pulp_ansible/galaxy
ProxyPassReverse /pulp_ansible/galaxy http://${pulp-api}/pulp_ansible/galaxy

Installation

It’s recommended to use the Pulp 3 Ansible Installer to install your plugin. Generally you can do this by configuring pulp_install_plugins variable with your Python package’s name. For example for pulp-file:

pulp_install_plugins:
  pulp-file: {}

Custom Installation Tasks

If your plugin requires any custom installation steps, we recommend using an Ansible Role prior to Pulp installation.

The easiest way to add custom installation tasks is to follow the Ansible Galaxy guide to create a new role with tasks that needs to be done and publish it on Ansible Galaxy.

Documentation will need to be added to the plugin installation instructions. See the RPM Plugin Documentation as an example.