Plugin API

Warning

The v0 plugin API is no longer the recommended way of developing new plugins for Tutor, starting from Tutor v13.2.0. See our plugin creation tutorial to learn more about the v1 plugin API. Existing v0 plugins will remain supported for some time but developers are encouraged to start migrating their plugins as soon as possible to make use of the new API. Please read the upgrade instructions to upgrade v0 plugins generated with the v0 plugin cookiecutter.

Plugins can affect the behaviour of Tutor at multiple levels. They can:

  • Add new settings or modify existing ones in the Tutor configuration (see config).

  • Add new templates to the Tutor project environment or modify existing ones (see patches, templates and hooks).

  • Add custom commands to the Tutor CLI (see command).

There exist two different APIs to create Tutor plugins: either with YAML files or Python packages. YAML files are more simple to create but are limited to just configuration and template patches.

config

The config attribute is used to modify existing and add new configuration parameters:

  • config["add"] are key/values that should be added to the user-specific config.yml configuration. Add there the passwords, secret keys, and other values that do not have a reasonable default value for all users.

  • config["defaults"] are default key/values for this plugin. These values can be accessed even though they are not added to the config.yml user file. Users can override them manually with tutor config save --set ....

  • config["set"] are existing key/values that should be modified. Be very careful what you add there! Different plugins may define conflicting values for some parameters.

“add” and “defaults” key names will be automatically prefixed with the plugin name, in upper case.

Example:

config = {
    "add": {
        "SECRET_KEY": "{{ 8|random_string }}"
    }
    "defaults": {
        "DOCKER_IMAGE": "username/imagename:latest",
    },
    "set": {
        "MASTER_PASSWORD": "h4cked",
    },
}

This configuration from the “myplugin” plugin will set the following values:

  • MYPLUGIN_SECRET_KEY: an 8-character random string will be generated and stored in the user configuration.

  • MYPLUGIN_DOCKER_IMAGE: this value will by default not be stored in config.yml, but tutor config printvalue MYPLUGIN_DOCKER_IMAGE will print username/imagename:latest.

  • MASTER_PASSWORD will be set to h4cked. Needless to say, plugin developers should avoid doing this.

patches

Plugin patches affect the rendered environment templates. In many places the Tutor templates include calls to {{ patch("patchname") }}. This grants plugin developers the possibility to modify the content of rendered templates. Plugins can add content in these places by adding values to the patches attribute. See Template patches for the complete list available patches.

Example:

patches = {
    "local-docker-compose-services": """redis:
image: redis:latest"""
}

This will add a Redis instance to the services run with tutor local commands.

Note

In Python plugins, remember that patches can be a callable function instead of a static dict value. One can use this to dynamically load a list of patch files from a folder.

hooks

Hooks are actions that are run during the lifetime of the platform. For instance, hooks are used to trigger database initialisation and migrations. Each hook has a different specification.

init

The services that will be run during initialisation should be added to the init hook, for instance for database creation and migrations.

Example:

hooks = {
  "init": ["myservice1", "myservice2"]
}

During initialisation, “myservice1” and “myservice2” will be run in sequence with the commands defined in the templates myplugin/hooks/myservice1/init and myplugin/hooks/myservice2/init.

To initialise a “foo” service, Tutor runs the “foo-job” service that is found in the env/local/docker-compose.jobs.yml file. By default, Tutor comes with a few services in this file: mysql-job, lms-job, cms-job. If your plugin requires running custom services during initialisation, you will need to add them to the docker-compose.jobs.yml template. To do so, just use the “local-docker-compose-jobs-services” patch.

In Kubernetes, the approach is the same, except that jobs are implemented as actual job objects in the k8s/jobs.yml template. To add your services there, your plugin should implement the “k8s-jobs” patch.

pre-init

This hook will be executed just before the init hooks. Otherwise, the specs are identical. This is useful for creating databases or other resources that will be required during initialisation, for instance.

build-image

This is a hook that will be run to build a docker image for the requested service.

Example:

hooks = {
    "build-image": {"myimage": "myimage:latest"}
}

With this hook, users will be able to build the myimage:latest docker image by running:

tutor images build myimage

or:

tutor images build all

This assumes that there is a Dockerfile file in the myplugin/build/myimage subfolder of the plugin templates directory.

remote-image

This hook allows pulling/pushing images from/to a docker registry.

Example:

hooks = {
    "remote-image": {"myimage": "myimage:latest"},
}

With this hook, users will be able to pull and push the myimage:latest docker image by running:

tutor images pull myimage
tutor images push myimage

or:

tutor images pull all
tutor images push all

templates

To define plugin-specific hooks, a plugin should also have a template directory that includes the plugin hooks. The templates attribute should point to that directory.

Example:

import os
templates = os.path.join(os.path.abspath(os.path.dirname(__file__)), "templates")

With the above declaration, you can store plugin-specific templates in the templates/myplugin folder next to the plugin.py file.

In Tutor, templates are Jinja2-formatted files that will be rendered in the Tutor environment (the $(tutor config printroot)/env folder) when running tutor config save. The environment files are overwritten every time the environment is saved. Plugin developers can create templates that make use of the built-in Jinja2 API. In addition, a couple of additional filters are added by Tutor:

  • common_domain: Return the longest common name between two domain names. Example: {{ "studio.demo.myopenedx.com"|common_domain("lms.demo.myopenedx.com") }} is equal to “demo.myopenedx.com”.

  • encrypt: Encrypt an arbitrary string. The encryption process is compatible with htpasswd verification.

  • list_if: In a list of (value, condition) tuples, return the list of value for which the condition is true.

  • long_to_base64: Base-64 encode a long integer.

  • iter_values_named: Yield the values of the configuration settings that match a certain pattern. Example: {% for value in iter_values_named(prefix="KEY", suffix="SUFFIX")%}...{% endfor %}. By default, only non-empty values are yielded. To iterate also on empty values, pass the allow_empty=True argument.

  • patch: See patches.

  • random_string: Return a random string of the given length composed of ASCII letters and digits. Example: {{ 8|random_string }}.

  • reverse_host: Reverse a domain name (see reference). Example: {{ "demo.myopenedx.com"|reverse_host }} is equal to “com.myopenedx.demo”.

  • rsa_import_key: Import a PEM-formatted RSA key and return the corresponding object.

  • rsa_private_key: Export an RSA private key in PEM format.

  • walk_templates: Iterate recursively over the templates of the given folder. For instance:

    {% for file in "apps/myplugin"|walk_templates %}
    ...
    {% endfor %}
    

When saving the environment, template files that are stored in a template root will be rendered to the environment folder. The following files are excluded:

  • Binary files with the following extensions: .ico, .jpg, .png, .ttf

  • Files that are stored in a folder named “partials”, or one of its subfolders.

command

Python plugins can provide a custom command line interface. The command attribute is assumed to be a click.Command object, and you typically implement them using the click.command decorator.

You may also use the click.pass_obj decorator to pass the CLI context, such as when you want to access Tutor configuration settings from your command.

Example:

import click
from tutor import config as tutor_config

@click.command(help="I'm a plugin command")
@click.pass_obj
def command(context):
    config = tutor_config.load(context.root)
    lms_host = config["LMS_HOST"]
    click.echo("Hello from myplugin!")
    click.echo(f"My LMS host is {lms_host}")

Any user who installs the myplugin plugin can then run:

$ tutor myplugin
Hello from myplugin!
My LMS host is demo.openedx.overhang.io

You can even define subcommands by creating command groups:

import click

@click.group(help="I'm a plugin command group")
def command():
    pass

@command.command(help="I'm a plugin subcommand")
def dosomething():
    click.echo("This subcommand is awesome")

This would allow any user to see your sub-commands:

$ tutor myplugin
Usage: tutor myplugin [OPTIONS] COMMAND [ARGS]...

  I'm a plugin command group

Commands:
  dosomething         I'm a plugin subcommand

and then run them:

$ tutor myplugin dosomething
This subcommand is awesome

See the official click documentation for more information.