The Glance chapter in the Folsom getting started guide includes a diagram. https://access.redhat.com/knowledge/docs/resources/docs/en-US/Red_Hat_OpenStack_Preview/2/html/Getting_Started_Guide/images/services3.png The current version of the diagram is not fully accurate for the architecture of Glance in Folsom. It is accurate for the glance v1 API. If the v2 glance API is enabled (which it is by default), the glance-api service talks to the database, as well.