Introduction to OpenStack Image services
The OpenStack Image service, otherwise known as Glance, is a service that allows users to register, discover, and retrieve virtual machine images for use in an OpenStack cloud. Images made available through the OpenStack Image service can be stored in a variety of formats and backend locations, from local filesystem storage to distributed filesystems such as OpenStack Object Storage (Swift) and Ceph.
The OpenStack Image service is composed of two major components: the glance-api service and the glance-registry service. Users interface with the glance-api service indirectly when performing commands to create, list, delete, or otherwise manage images using OpenStack clients. The glance-registry service is responsible for connecting to the backend database and storing or retrieving images.