The Image Service includes the following components:
glance-api. Accepts Image API calls for image discovery, retrieval, and storage.glance-registry. Stores, processes, and retrieves metadata about images. Metadata includes size, type, and so on.Database. Stores image metadata. You can choose your database depending on your preference. Most deployments use MySQL or SQlite.
Storage repository for image files. In Figure 1.2, “Logical architecture”, the Object Storage Service is the image repository. However, you can configure a different repository. The Image Service supports normal file systems, RADOS block devices, Amazon S3, and HTTP. Some choices provide only read-only usage.
A number of periodic processes run on the Image Service to support caching. Replication services ensures consistency and availability through the cluster. Other periodic processes include auditors, updaters, and reapers.
As shown in the section called “Conceptual architecture”, the Image Service is central to the overall IaaS picture. It accepts API requests for images or image metadata from end users or Compute components and can store its disk files in the Object Storage Service.
