503 Service Unavailable
Temporarily down or overloaded — deploys, maintenance, circuit breakers.
503Server error
- What it means
- Temporarily down or overloaded — deploys, maintenance, circuit breakers.
- In practice
- Unlike 502, 503 is usually sent on purpose: maintenance mode, an overloaded pool shedding load, a circuit breaker that has opened. It is the polite outage code — pair it with Retry-After so clients know when to come back. If a health checker sees a 503, the service is telling you it knows it is unwell.
- Whose problem is it?
- The server (or something behind it). The request may have been fine.
Often confused with