The server is currently unable to handle the request due to a temporary overload or scheduled maintenance, which will likely be alleviated after some delay. The server MAY send a Retry-After header field1 to suggest an appropriate amount of time for the client to wait before retrying the request. Note: The existence of the status code does not imply that a server has to use it when becoming overloaded. Some servers might simply refuse the connection. 1 Retry-After RFC7231 Section 7.1.3 Source: RFC7231 Section 6.6.4 CODE REFERENCES Rails HTTP Status Symbol :service_unavailable Go HTTP Status Constant http.StatusServiceUnavailable Symfony HTTP Status Constant Response::HTTP_SERVICE_UNAVAILABLE Python2 HTTP Status Constant httplib.SERVICE_UNAVAILABLE Python3+ HTTP Status Constant http.client.SERVICE_UNAVAILABLE Python3.5+ HTTP Status Constant http.HTTPStatus.SERVICE_UNAVAILABLE