The OpenStack Image Service (glance) enables users to discover, register, and retrieve virtual machine images. It offers a REST API that enables you to query virtual machine image metadata and retrieve an actual image. You can store virtual machine images made available through the Image Service in a variety of locations, from simple file systems to object-storage systems like OpenStack Object Storage. For simplicity, this guide describes configuring the Image Service to use the file back end, which uploads and stores in a directory on the controller node hosting the Image Service. By default, this directory is /var/lib/glance/images/. Before you proceed, ensure that the controller node has at least several gigabytes of space available in this directory. For information on requirements for other back ends, see Configuration Reference.