HTTP 503 Service Unavailable indicates the server is temporarily unable to handle the request due to overload or maintenance. Unlike 500 (unexpected error) or 502 (bad upstream), 503 explicitly means 'come back later.' The server SHOULD include a Retry-After header indicating when the service is expected to be available. This is the correct status for planned maintenance windows, deployment rollouts, and circuit breaker activations.
Response includes the status code, standard headers (including Content-Type), and a small diagnostic JSON body describing the request and returned status.
Simulator URL (copy in the app after load — not a normal link):
https://httpstatus.com/api/status/503
Example request:
curl -i "https://httpstatus.com/api/status/503"