The OpenStack Image Service discovers, registers, and retrieves virtual machine images. The service also includes a RESTful API that allows you to query VM image metadata and retrieve the actual image with HTTP requests. For more information about the API, see the OpenStack API Complete Reference and the Python API. The OpenStack Image Service can be controlled using a command-line tool. For more information about the using OpenStack Image command-line tool, see the Manage Images section in the OpenStack End User Guide. Virtual images that have been made available through the Image Service can be stored in a variety of ways. In order to use these services, you must have a working installation of the Image Service, with a working endpoint, and users that have been created in OpenStack Identity. Additionally, you must meet the environment variables required by the Compute and Image Service clients. The Image Service supports these back-end stores: File system The OpenStack Image Service stores virtual machine images in the file system back end by default. This simple back end writes image files to the local file system. Object Storage service The OpenStack highly available service for storing objects. S3 The Amazon S3 service. HTTP OpenStack Image Service can read virtual machine images that are available on the Internet using HTTP. This store is read only. Rados block device (RBD) Stores images inside of a Ceph storage cluster using Ceph's RBD interface. GridFS Stores images using MongoDB.