Based on your edit about getting the public IP: Most firewall/routers are not configured to do this operation by default (called Hairpinning). If you request your firewall/router’s external IP address from the internal network you won’t get a response unless Hairpinning is enabled and some devices don’t allow you to do that. If you have an internal dns server, you should override the internal dns to return the private ip address so it goes to your nginx reverse proxy instead of the firewall/router.