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3.8 KiB
ReStructuredText
86 lines
3.8 KiB
ReStructuredText
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Copyright 2015 OpenStack Foundation
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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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==================
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Basic architecture
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==================
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OpenStack Glance has a client-server architecture that provides a REST API
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to the user through which requests to the server can be performed.
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A Glance Domain Controller manages the internal server operations
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that is divided into layers. Specific tasks are implemented
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by each layer.
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All the file (Image data) operations are performed using
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glance_store library, which is responsible for interaction with external
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storage back ends and (or) local filesystem(s). The glance_store library
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provides a uniform interface to access the backend stores.
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Glance uses a central database (Glance DB) that is shared amongst all
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the components in the system and is sql-based by default. Other types
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of database backends are somewhat supported and used by operators
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but are not extensively tested upstream.
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.. figure:: ../images/architecture.png
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:figwidth: 100%
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:align: center
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:alt: OpenStack Glance Architecture Diagram.
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Consists of 5 main blocks: "Client" "Glance" "Keystone"
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"Glance Store" and "Supported Storages".
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Glance block exposes a REST API. The REST API makes use of the
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AuthZ Middleware and a Glance Domain Controller, which contains
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Auth, Notifier, Policy, Quota, Location and DB. The Glance Domain
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Controller makes use of the Glance Store (which is external to the
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Glance block), and (still within the Glance block) it makes use of
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the Database Abstraction Layer, and (optionally) the Registry Layer.
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The Registry Layer makes use of the Database Abstraction Layer. The
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Database abstraction layer exclusively makes use of the Glance
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Database.
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The Client block makes use of the Rest API (which exists in the
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Glance block) and the Keystone block.
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The Glance Store block contains AuthN which makes use of the
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Keystone block, and it also contains Glance Store Drivers, which
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exclusively makes use of each of the storage systems in the
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Supported Storages block. Within the Supported Storages block,
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there exist the following storage systems, none of which make use
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of anything else: Filesystem, Swift, Ceph, "ellipses", Sheepdog.
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A complete list is given by the currently available drivers in
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glance_store/_drivers.
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.. centered:: Image 1. OpenStack Glance Architecture
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Following components are present in the Glance architecture:
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* **A client** - any application that makes use of a Glance server.
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* **REST API** - Glance functionalities are exposed via REST.
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* **Database Abstraction Layer (DAL)** - an application programming interface
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(API) that unifies the communication between Glance and databases.
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* **Glance Domain Controller** - middleware that implements the main
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Glance functionalities such as authorization, notifications, policies,
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database connections.
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* **Glance Store** - used to organize interactions between Glance and various
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data stores.
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* **Registry Layer** - optional layer that is used to organise secure
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communication between the domain and the DAL by using a separate service.
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.. include:: ../deprecate-registry.inc
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