Chapter 3. Understanding Glance

Glance is the newest OpenStack service. First debuting in the Bexar release, Glance provides a catalog service for storing and querying virtual disk images. Glance has been designed to be a standalone service for those needing to organize large sets of virtual disk images. However, when used along with Nova and Swift, it provides an end-to-end solution for cloud disk image management.

Architecture

There are three pieces to Glance architecture: glance-api, glance-registry, and the image store. As you can probably guess, glance-api accepts API calls, much like nova-api, and the actual image blobs are placed in the image store. The glance-registry stores and retrieves metadata about images. The image store can be a number of different object stores, including Swift. Figure 3-1 illustrates Glance’s logical architecture.

Glance Logical Architecture

Figure 3-1. Glance Logical Architecture

glance-api is similar in functionality to nova-api, in that it accepts incoming API requests and then communicates with the other components (glance-registry and the image store) to facilitate querying, retrieving, uploading, or deleting images. By default, glance-api listens on port 9292.

Caution

In the Cactus release, Glance lacks authentication and authorization, making it unsuitable for direct end user usage except in tightly controlled environments. The best way to use this is “behind” Nova, where ...

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