curl: (52) Empty reply from server

Common causes

• Sending plain HTTP to a port that expects TLS, such as http://host:443.
• The application crashed or hit a fatal error before writing a response.
• A proxy, WAF or rate limiter dropped the request silently.
• A service in a container listening only on 127.0.0.1, behind a port mapping that accepts the connection but has nothing to forward to.

How to fix it

1. Check the scheme matches the port: https:// for TLS ports.
2. Look at the application and proxy logs for crashes at the time of the request.
3. Run curl -v to confirm the request was sent and nothing came back.
4. Make services inside containers listen on 0.0.0.0, not 127.0.0.1.