The Glance architecture has stayed relatively stable since the Cactus release. The biggest architectural change has been the addition of authentication, which was added in the Diablo release. Just as a quick reminder, Glance has four main parts to it:
glance-apiaccepts Image API calls for image discovery, image retrieval and image storageglance-registrystores, processes and retrieves metadata about images (size, type, etc.)A database to store the image metadata. Like Nova, you can choose your database depending on your preference (but most people use MySQL or SQlite).
A storage repository for the actual image files. In the diagram, I have shown the most likely configuration (using Swift as the image repository), but this is configurable. In addition to Swift, Glance supports normal filesystems, RADOS block devices, Amazon S3 and HTTP. Be aware that some of these choices are limited to read-only usage.
There are also a number of periodic process which run on Glance to support caching. The most important of these is the replication services, which ensures consistency and availability through the cluster. Other periodic processes include auditors, updaters and reapers.
As you can see from the diagram, Glance serves a central role to the overall IaaS picture. It accepts API requests for images (or image metadata) from end users or Nova components and can store it's disk files in
