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The Pike and Queens release notes recommend against running Glance under uwsgi. Add a note to the install guide as another location where this information is available. Change-Id: I3aa61ea45a3d3edaa5b8062813fc3e1388556f9f
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======================
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Image service overview
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======================
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The Image service (glance) enables users to discover,
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register, and retrieve virtual machine images. It offers a
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:term:`REST <RESTful>` API that enables you to query virtual
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machine image metadata and retrieve an actual image.
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You can store virtual machine images made available through
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the Image service in a variety of locations, from simple file
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systems to object-storage systems like OpenStack Object Storage.
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.. important::
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For simplicity, this guide describes configuring the Image service to
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use the ``file`` back end, which uploads and stores in a
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directory on the controller node hosting the Image service. By
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default, this directory is ``/var/lib/glance/images/``.
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Before you proceed, ensure that the controller node has at least
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several gigabytes of space available in this directory. Keep in
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mind that since the ``file`` back end is often local to a controller
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node, it is not typically suitable for a multi-node glance deployment.
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For information on requirements for other back ends, see
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`Configuration Reference <../configuration/index.html>`__.
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The OpenStack Image service is central to Infrastructure-as-a-Service
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(IaaS). It accepts API requests for disk or server images, and
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metadata definitions from end users or OpenStack Compute
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components. It also supports the storage of disk or server images on
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various repository types, including OpenStack Object Storage.
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A number of periodic processes run on the OpenStack Image service to
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support caching. Replication services ensure consistency and
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availability through the cluster. Other periodic processes include
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auditors, updaters, and reapers.
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The OpenStack Image service includes the following components:
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glance-api
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Accepts Image API calls for image discovery, retrieval, and storage.
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.. note::
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An OpenStack Community Goal in the Pike release was `Control Plane API
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endpoints deployment via WSGI`_. As currently constituted, however,
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glance-api is **not suitable** to be run in such a configuration. Instead
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we recommend that Glance be run in the traditional manner as a standalone
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server. See the "Known Issues" section of the `Glance Release Notes`_ for
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the Pike and Queens releases for more information.
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.. _`Control Plane API endpoints deployment via WSGI`: https://governance.openstack.org/tc/goals/pike/deploy-api-in-wsgi.html
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.. _`Glance Release Notes`: https://docs.openstack.org/releasenotes/glance/index.html
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glance-registry
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Stores, processes, and retrieves metadata about images. Metadata
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includes items such as size and type.
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.. warning::
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The registry is a private internal service meant for use by
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OpenStack Image service. Do not expose this service to users.
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.. include:: ../deprecate-registry.inc
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Database
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Stores image metadata and you can choose your database depending on
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your preference. Most deployments use MySQL or SQLite.
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Storage repository for image files
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Various repository types are supported including normal file
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systems (or any filesystem mounted on the glance-api controller
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node), Object Storage, RADOS block devices, VMware datastore,
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and HTTP. Note that some repositories will only support read-only
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usage.
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Metadata definition service
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A common API for vendors, admins, services, and users to meaningfully
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define their own custom metadata. This metadata can be used on
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different types of resources like images, artifacts, volumes,
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flavors, and aggregates. A definition includes the new property's key,
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description, constraints, and the resource types which it can be
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associated with.
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