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Quick Guide to Getting Started with Glance
==========================================

Glance is a server that provides the following services:

* Ability to store and retrieve virtual machine images
* Ability to store and retrieve metadata about these virtual machine images
* FUTURE: Convert a virtual machine image from one format to another
* FUTURE: Help caching proxies such as Varnish or Squid cache machine images

Communication with Glance occurs via a REST-like HTTP interface.

However, Glance includes a :doc:`Client <client>` class that makes working with Glance
easy and straightforward.

In the Cactus release, there will be also command-line tools for
interacting with Glance.

Overview of Glance Architecture
-------------------------------

There are two main parts to Glance's architecture:

* Glance API server
* Glance Registry server(s)

Glance API Server
*****************

The API server is the main interface for Glance. It routes requests from
clients to registries of image metadata and to its **backend stores**, which
are the mechanisms by which Glance actually saves incoming virtual machine
images.

The backend stores that Glance can work with are as follows:

* **Swift**

  Swift is the highly-available object storage project in OpenStack. More
  information can be found about Swift `here <http://swift.openstack.org>`_.

* **Filesystem**

  The default backend that Glance uses to store virtual machine images
  is the filesystem backend. This simple backend writes image files to the
  local filesystem.

* **S3**

  This backend allows Glance to store virtual machine images in Amazon's
  S3 service.

* **HTTP**

  Glance can read virtual machine images that are available via
  HTTP somewhere on the Internet.  This store is **readonly**

Glance Registry Servers
***********************

Glance registry servers are servers that conform to the Glance Registry API.
Glance ships with a reference implementation of a registry server that
complies with this API (``glance-registry``).

For more details on Glance's architecture see :doc:`here <architecture>`. For
more information on what a Glance registry server is, see
:doc:`here <registries>`.