HTTP 503 Service Unavailable

Description

The 503 Service Unavailable status code indicates that the server is currently unable to handle the request due to a temporary overloading or scheduled maintenance, which will likely be alleviated after some delay. 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. The existence of the 503 status code does not imply that a server has to use it when becoming overloaded; some servers may simply refuse the connection. Unlike 500, which indicates an internal error, 503 explicitly signals a temporary condition that is expected to resolve.

When Is It Used?

Returned during planned maintenance, server overload, or temporary capacity issues. Cloud platforms may return 503 during scaling events. Commonly used with a Retry-After header to tell clients when to try again.

Example Response

HTTP/1.1 503 Service Unavailable
Retry-After: 300
Content-Type: application/json

{"error": "service_unavailable", "message": "The server is undergoing maintenance. Please try again in 5 minutes."}

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