frp is a common tool that used to set up HTTP or TCP tunnel between 2 networks. A usual use case is set up a tunnel between home server and public server so that you can access your internal service on the Internet.
This page assumes that:
1. Your frp server is openning at "frps.example.com"
2. You have a Kubernetes Service names "demo-service", you can access it via "demo-service:8080" inside the cluster