I have a server with Ubuntu server and UFW firewall. Server runs docker, and in docker two containers. One is a proxy server, another is some other service with WebUI on port 42111. This service has no ability for authentication on WebUI.
So I want to somehow block connections to WebUI on port 42111 from the Internet (which is by default with UFW), but allow connections that come from the proxy server on the machine.
How do I set it up properly?