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9.1 KiB
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279 lines
9.1 KiB
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Copyright 2011-2012 OpenStack, LLC
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All Rights Reserved.
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Licensed under the Apache License, Version 2.0 (the "License"); you may
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not use this file except in compliance with the License. You may obtain
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a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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License for the specific language governing permissions and limitations
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under the License.
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Keystone Architecture
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=====================
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Much of the design is precipitated from the expectation that the auth backends
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for most deployments will actually be shims in front of existing user systems.
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------------
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The Services
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------------
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Keystone is organized as a group of internal services exposed on one or many
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endpoints. Many of these services are used in a combined fashion by the
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frontend, for example an authenticate call will validate user/tenant
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credentials with the Identity service and, upon success, create and return a
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token with the Token service.
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Identity
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--------
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The Identity service provides auth credential validation and data about Users,
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Tenants and Roles, as well as any associated metadata.
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In the basic case all this data is managed by the service, allowing the service
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to manage all the CRUD associated with the data.
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In other cases, this data is pulled, by varying degrees, from an authoritative
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backend service. An example of this would be when backending on LDAP. See
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`LDAP Backend` below for more details.
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Token
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-----
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The Token service validates and manages Tokens used for authenticating requests
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once a user/tenant's credentials have already been verified.
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Catalog
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-------
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The Catalog service provides an endpoint registry used for endpoint discovery.
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Policy
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------
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The Policy service provides a rule-based authorization engine and the
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associated rule management interface.
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------------------------
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Application Construction
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------------------------
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Keystone is an HTTP front-end to several services. Like other OpenStack
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applications, this is done using python WSGI interfaces and applications are
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configured together using Paste_. The application's HTTP endpoints are made up
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of pipelines of WSGI middleware, such as::
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[pipeline:public_api]
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pipeline = token_auth admin_token_auth json_body debug ec2_extension public_service
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These in turn use a subclass of :mod:`keystone.common.wsgi.ComposingRouter` to
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link URLs to Controllers (a subclass of
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:mod:`keystone.common.wsgi.Application`). Within each Controller, one or more
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Managers are loaded (for example, see :mod:`keystone.catalog.core.Manager`),
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which are thin wrapper classes which load the appropriate service driver based
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on the keystone configuration.
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* Identity
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* :mod:`keystone.identity.core.TenantController`
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* :mod:`keystone.identity.core.UserController`
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* :mod:`keystone.identity.core.RoleController`
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* Catalog
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* :mod:`keystone.catalog.core.ServiceController`
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* :mod:`keystone.service.VersionController`
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* Token
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* :mod:`keystone.service.TokenController`
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* Misc
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* :mod:`keystone.service.ExtensionsController`
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At this time, the policy service and associated manager is not exposed as a URL
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frontend, and has no associated Controller class.
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.. _Paste: http://pythonpaste.org/
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----------------
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Service Backends
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----------------
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Each of the services can configured to use a backend to allow Keystone to fit a
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variety of environments and needs. The backend for each service is defined in
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the keystone.conf file with the key ``driver`` under a group associated with
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each service.
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A general class under each backend named ``Driver`` exists to provide an
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abstract base class for any implementations, identifying the expected service
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implementations. The drivers for the services are:
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* :mod:`keystone.identity.core.Driver`
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* :mod:`keystone.token.core.Driver`
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If you implement a backend driver for one of the keystone services, you're
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expected to subclass from these classes. The default response for the defined
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apis in these Drivers is to raise a :mod:`keystone.service.TokenController`.
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KVS Backend
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-----------
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A simple backend interface meant to be further backended on anything that can
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support primary key lookups, the most trivial implementation being an in-memory
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dict.
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Supports all features of the general data model.
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SQL Backend
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-----------
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A SQL based backend using SQLAlchemy to store data persistently. The
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keystone-manage command introspects the backends to identify SQL based backends
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when running "db_sync" to establish or upgrade schema. If the backend driver
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has a method db_sync(), it will be invoked to sync and/or migrate schema.
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PAM Backend
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-----------
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Extra simple backend that uses the current system's PAM service to authenticate,
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providing a one-to-one relationship between Users and Tenants with the `root`
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User also having the 'admin' role.
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Templated Backend
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-----------------
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Largely designed for a common use case around service catalogs in the Keystone
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project, a Catalog backend that simply expands pre-configured templates to
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provide catalog data.
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Example paste.deploy config (uses $ instead of % to avoid ConfigParser's
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interpolation)::
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[DEFAULT]
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catalog.RegionOne.identity.publicURL = http://localhost:$(public_port)s/v2.0
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catalog.RegionOne.identity.adminURL = http://localhost:$(public_port)s/v2.0
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catalog.RegionOne.identity.internalURL = http://localhost:$(public_port)s/v2.0
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catalog.RegionOne.identity.name = 'Identity Service'
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LDAP Backend
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------------
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The LDAP backend stored Users and Tenents in separate Subtrees. Roles are recorded
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as entries under the Tenants.
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----------
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Data Model
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----------
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Keystone was designed from the ground up to be amenable to multiple styles of
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backends and as such many of the methods and data types will happily accept
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more data than they know what to do with and pass them on to a backend.
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There are a few main data types:
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* **User**: has account credentials, is associated with one or more tenants
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* **Tenant**: unit of ownership in openstack, contains one or more users
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* **Role**: a first-class piece of metadata associated with many user-tenant pairs.
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* **Token**: identifying credential associated with a user or user and tenant
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* **Extras**: bucket of key-value metadata associated with a user-tenant pair.
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* **Rule**: describes a set of requirements for performing an action.
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While the general data model allows a many-to-many relationship between Users
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and Tenants and a many-to-one relationship between Extras and User-Tenant pairs,
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the actual backend implementations take varying levels of advantage of that
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functionality.
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----------------
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Approach to CRUD
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----------------
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While it is expected that any "real" deployment at a large company will manage
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their users, tenants and other metadata in their existing user systems, a
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variety of CRUD operations are provided for the sake of development and testing.
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CRUD is treated as an extension or additional feature to the core feature set
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in that it is not required that a backend support it. It is expected that
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backends for services that don't support the CRUD operations will raise a
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:mod:`keystone.exception.NotImplemented`.
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----------------------------------
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Approach to Authorization (Policy)
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----------------------------------
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Various components in the system require that different actions are allowed
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based on whether the user is authorized to perform that action.
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For the purposes of Keystone there are only a couple levels of authorization
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being checked for:
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* Require that the performing user is considered an admin.
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* Require that the performing user matches the user being referenced.
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Other systems wishing to use the policy engine will require additional styles
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of checks and will possibly write completely custom backends. Backends included
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in Keystone are:
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Rules
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-----
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Given a list of matches to check for, simply verify that the credentials
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contain the matches. For example::
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credentials = {'user_id': 'foo', 'is_admin': 1, 'roles': ['nova:netadmin']}
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# An admin only call:
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policy_api.enforce(('is_admin:1',), credentials)
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# An admin or owner call:
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policy_api.enforce(('is_admin:1', 'user_id:foo'), credentials)
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# A netadmin call:
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policy_api.enforce(('roles:nova:netadmin',), credentials)
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Credentials are generally built from the user metadata in the 'extras' part
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of the Identity API. So, adding a 'role' to the user just means adding the role
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to the user metadata.
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Capability RBAC
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---------------
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(Not yet implemented.)
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Another approach to authorization can be action-based, with a mapping of roles
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to which capabilities are allowed for that role. For example::
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credentials = {'user_id': 'foo', 'is_admin': 1, 'roles': ['nova:netadmin']}
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# add a policy
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policy_api.add_policy('action:nova:add_network', ('roles:nova:netadmin',))
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policy_api.enforce(('action:nova:add_network',), credentials)
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In the backend this would look up the policy for 'action:nova:add_network' and
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then do what is effectively a 'Simple Match' style match against the creds.
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