The OpenStack Image Service is central to Infrastructure-as-a-Service (IaaS) as shown in . It accepts API requests for disk or server images, and image metadata from end users or OpenStack Compute components. It also supports the storage of disk or server images on various repository types, including OpenStack Object Storage. A number of periodic processes run on the OpenStack Image Service to support caching. Replication services ensure consistency and availability through the cluster. Other periodic processes include auditors, updaters, and reapers. The OpenStack 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 items such as size and type. The registry is a private internal service meant for use by OpenStack Image Service. Do not disclose it to users. Database Stores image metadata and you can choose your database depending on your preference. Most deployments use MySQL or SQLite. Storage repository for image files Various repository types are supported including normal file systems, Object Storage, RADOS block devices, HTTP, and Amazon S3. Note that some repositories will only support read-only usage.