keystone/doc/source/extension_development.rst

Keystone Extensions Development Guide

General

This Extension Development Guide provides some mocked code to use as an Extension code base in the keystone/contrib/example folder.

• All Extensions must be created in the keystone/contrib folder.

• The new Extension code must be contained in a new folder under contrib.

• Whenever possible an Extension should follow the following directory structure convention:

  keystone/contrib/
  └── my_extension
      ├── backends (optional)
      │   ├── __init__.py (mandatory)
      │   └── sql.py (optional)
      │   └── kvs.py (optional)
      ├── migrate_repo (optional)
      │   ├── __init__.py (mandatory)
      │   ├── migrate.cfg (mandatory)
      │   └── versions (mandatory)
      │       ├── 001_create_tables.py (mandatory)
      │       └── __init__.py (mandatory)
      ├── __init__.py (mandatory)
      ├── core.py (mandatory)
      ├── controllers.py (mandatory for API Extension)
      └── routers.py (mandatory for API Extension)

• If the Extension implements an API Extension the controllers.py and routers.py must be present and correctly handle the API Extension requests and responses.

• If the Extension implements backends a backends folder should exist. Backends are defined to store data persistently and can use a variety of technologies. Please see the Backends section in this document for more info.

• If the Extension adds data structures, then a migrate_repo folder should exist.

• If configuration changes are required/introduced in the keystone.conf.sample file, these should be kept disabled as default and have their own section.

• If configuration changes are required/introduced in the keystone-paste.ini, the new filter must be declared.

• The module may register to listen to events by declaring the corresponding callbacks in the core.py file.

• The new extension should be disabled by default (it should not affect the default application pipelines).

Modifying the keystone.conf.sample File

In the case an Extension needs to change the keystone.conf.sample file, it must follow the config file conventions and introduce a dedicated section.

Example:

[example]
driver = keystone.contrib.example.backends.sql.mySQLClass

[my_other_extension]
extension_flag = False

The Extension parameters expressed should be commented out since, by default, extensions are disabled.

Example:

[example]
#driver = keystone.contrib.example.backends.sql.mySQLClass

[my_other_extension]
#extension_flag = False

In case the Extension is overriding or re-implementing an existing portion of Keystone, the required change should be commented in the configuration.rst but not placed in the keystone.conf.sample file to avoid unnecessary confusion.

Modifying the keystone-paste.ini File

In the case an Extension is augmenting a pipeline introducing a new filter and/or APIs in the OS namespace, a corresponding filter: section is necessary to be introduced in the keystone-paste.ini file. The Extension should declare the filter factory constructor in the ini file.

Example:

[filter:example]
paste.filter_factory = keystone.contrib.example.routers:ExampleRouter.
factory

The filter must not be placed in the pipeline and treated as optional. How to add the extension in the pipeline should be specified in detail in the configuration.rst file.

Package Constructor File

The __init__.py file represents the package constructor. Extension needs to import what is necessary from the core.py module.

Example:

from keystone.contrib.example.core import *

Core

The core.py file represents the main module defining the data structure and interface. In the Model View Control (MVC) model it represents the Model part and it delegates to the Backends the data layer implementation.

In case the core.py file contains a Manager and a Driver it must provide the dependency injections for the Controllers and/or other modules using the Manager. A good practice is to call the dependency extension_name_api.

Example:

@dependency.provider('example_api')
class Manager(manager.Manager):

Routers

routers.py have the objective of routing the HTTP requests and direct them to the correct method within the Controllers. Extension routers are extending the wsgi.ExtensionRouter.

Example:

from keystone.common import wsgi
from keystone.contrib.example import controllers


class ExampleRouter(wsgi.ExtensionRouter):

    PATH_PREFIX = '/OS-EXAMPLE'

    def add_routes(self, mapper):
        example_controller = controllers.ExampleV3Controller()
        mapper.connect(self.PATH_PREFIX + '/example',
                       controller=example_controller,
                       action='do_something',
                       conditions=dict(method=['GET']))

Controllers

controllers.py have the objective of handing requests and implement the Extension logic. Controllers are consumers of 'Managers' API and must have all the dependency injections required. Controllers are extending the V3Controller class.

Example:

@dependency.requires('identity_api', 'example_api')
class ExampleV3Controller(controller.V3Controller):
    pass

Backends

The backends folder provides the model implementations for the different backends supported by the Extension. See General above for an example directory structure.

If a SQL backend is provided, in the sql.py backend implementation it is mandatory to define the new table(s) that the Extension introduces and the attributes they are composed of.

For more information on backends, refer to the Keystone Architecture documentation.

Example:

class ExampleSQLBackend(sql.ModelBase, sql.DictBase):
    """example table description."""
    __tablename__ = 'example_table'
    attributes = ['id', 'type', 'extra']

    example_id = sql.Column(sql.String(64),
                            primary_key=True,
                            nullable=False)
    ...

SQL Migration Repository

In case the Extension is adding SQL data structures, these must be stored in separate tables and must not be included in the migrate_repo of the core Keystone. Please refer to the migrate.cfg file to configure the Extension repository.

In order to create the Extension tables and their attributes, a db_sync command must be executed.

Example:

$ ./bin/keystone-manage db_sync --extension example

Event Callbacks

Extensions may provide callbacks to Keystone (Identity) events. Extensions must provide the list of events of interest and the corresponding callbacks. Events are issued upon successful creation, modification, and deletion of the following Keystone resources:

• group
• project
• role
• user

The extension's Manager class must contain the event_callbacks attribute. It is a dictionary listing as keys those events that are of interest and the values should be the respective callbacks. Event callback registration is done via the dependency injection mechanism. During dependency provider registration, the dependency.provider decorator looks for the event_callbacks class attribute. If it exists the event callbacks are registered accordingly. In order to enable event callbacks, the extension's Manager class must also be a dependency provider.

Example:

# Since this is a dependency provider. Any code module using this or any
# other dependency provider (uses the dependency.provider decorator)
# will be enabled for the attribute based notification

@dependency.provider('example_api')
class ExampleManager(manager.Manager):
    """Example Manager.

    See :mod:`keystone.common.manager.Manager` for more details on
    how this dynamically calls the backend.

    """

    def __init__(self):
        self.event_callbacks = {
            # Here we add the event_callbacks class attribute that
            # calls project_deleted_callback when a project is deleted.
            'deleted': {
                'project': [
                    self.project_deleted_callback]}}
        super(ExampleManager, self).__init__(
            'keystone.contrib.example.core.ExampleDriver')

    def project_deleted_callback(self, context, message):
        # cleanup data related to the deleted project here

A callback must accept the following parameters:

• service - the service information (e.g. identity)
• resource_type - the resource type (e.g. project)
• operation - the operation (updated, created, deleted)
• payload - the actual payload info of the resource that was acted on

Current callback operations:

• created
• deleted
• updated

Example:

def project_deleted_callback(self, service, resource_type, operation,
                             payload):