Glance is a server that provides the following services:
Communication with Glance occurs via a REST-like HTTP interface.
However, Glance includes a 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.
There are two main parts to Glance’s architecture:
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.
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 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 here. For more information on what a Glance registry server is, see here.