503Service Unavailable
503 Service Unavailable means the server is currently unable to handle the request because of temporary overload or scheduled maintenance. It may include Retry-After to say when to try again.
What does it mean?
The condition is expected to be temporary. A 503 does not imply that the server must use it when overloaded; some servers simply refuse the connection.
Use 500 for unexpected bugs. Use 502 or 504 when a gateway or upstream is the problem.
When does it happen?
- Scheduled maintenance.
- A traffic spike or resource exhaustion.
- A critical dependency is down.
- A deployment is in progress.
How do you fix it?
If you run the server
- Send Retry-After when you can estimate the downtime.
- Serve a maintenance page that explains the state and when to return.
- Do not use 503 for a permanent failure; use a specific 5xx or 4xx code.
If you are just visiting
- Wait and retry; the server said it is temporary.
- Check the site's status page if it has one.
