503 Service Unavailable

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 503 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

503 Code references

Go HTTP Status Constant http.StatusServiceUnavailable
Python3+ HTTP Status Constant http.client.SERVICE_UNAVAILABLE
Python3.5+ HTTP Status Constant http.HTTPStatus.SERVICE_UNAVAILABLE
Rails HTTP Status Symbol :service_unavailable
Symfony HTTP Status Constant Response::HTTP_SERVICE_UNAVAILABLE

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