The OpenStack Compute API is defined as a ReSTful HTTP service. The API takes advantage of all aspects of the HTTP protocol (methods, URIs, media types, response codes, etc.) and providers are free to use existing features of the protocol such as caching, persistent connections, and content compression among others. For example, providers who employ a caching layer may respond with a 203 when a request is served from the cache instead of a 200. Additionally, providers may offer support for conditional GET requests using ETags, or they may send a redirect in response to a GET request. Clients should be written to account for these differences.
Providers can return information identifying requests in HTTP response headers, for example, to facilitate communication between the provider and client users.
