Synology NAS Reverse Proxy 502 Error: How to Fix It

Q: What does reverse proxy 502 error mean on Synology NAS?

A 502 error means your Synology NAS reverse proxy cannot reach the backend service you're trying to access. The service is either down, unreachable, or configured with incorrect port settings.

Q: How do I check if my backend service is running?

Try accessing the service directly using its IP address and port number in a web browser. If it's a Synology package, check Package Center to see if it's running. For external services, check the service status on the target server.

Q: Can incorrect SSL certificates cause 502 errors?

Yes, if your reverse proxy is configured for HTTPS but the backend service has SSL certificate issues or doesn't support HTTPS, you'll get 502 errors. Verify SSL settings match between the proxy and backend service.

Q: Why does my reverse proxy work sometimes but not others?

Intermittent 502 errors often indicate the backend service is unstable, running out of resources, or has connection limits. Check the service's resource usage and configuration for maximum connections or memory limits.

Q: How do I fix 502 errors for Docker containers behind reverse proxy?

Ensure the Docker container is running and accessible on the correct port. Check that the container's internal port mapping matches your reverse proxy destination port, and verify the container isn't restarting due to errors.

Abstract

The Synology reverse proxy 502 error occurs when your NAS cannot communicate with the backend service you're trying to access. This typically happens when a service is down, misconfigured, or using the wrong port settings.