503 Service Unavailable

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..

Takeaways

1. 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.
2. The server may send a Retry-After header field to suggest an appropriate amount of time for the client to wait before retrying the request.

Information

Common causes are a server that is down for maintenance or that is overloaded. This response should be used for temporary conditions and the Retry-After HTTP header should, if possible, contain the estimated time for the recovery of the service.

Caching-related headers that are sent along with this response should be taken care of, as a 503 status is often a temporary condition and responses shouldn't usually be cached.