503
Server Error
503 Service Unavailable
The server is temporarily unable to handle the request.
Definition (RFC 9110)
HTTP status code 503 503 Service Unavailable is defined in RFC 9110 (HTTP Semantics), Section 15.6.4 — the current authoritative specification for HTTP semantics, published June 2022, which obsoletes the older RFC 7231 and RFC 2616.
Description
The 503 Service Unavailable status code indicates that the server is currently unable to handle the request due to temporary overload or scheduled maintenance. The response may include a Retry-After header indicating when the service is expected to be available.
Common Causes
- Server maintenance
- Server overload
- Application deployment in progress
- Rate limiting at infrastructure level
- Resource exhaustion (CPU, memory, connections)
How to Fix
- Wait and retry the request
- Check server status page
- Scale server resources
- Implement graceful degradation
- Set up load balancing
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