Introduction

Glance image service is a project that offers images as a service, it enables users to discover, register, and retrieve operating system disk images from which users can launch OpenStack instances. The image service offers a REST API that enables users to query virtual machine disk images and metadata. Virtual machine disk images can be stored on various datastore backends, such as local filesystem, NFS, Ceph, Swift, and others.

Glance consists of the following two services:

• glance-api accepts REST API calls for image discovery, retrieval, and creation. It stores and retrieves disk images from storage backend. The Image Service supports a variety of backends, including local filesystems, object storage, Ceph RADOS block devices, HTTP, and Amazon S3.
• glance-registry stores, processes, and retrieves metadata of disk images from the backend datastore storage device. Metadata includes some items, such as size and type.