OpenVPN and WireGuard server on GitHub Actions: representative NAT traversal

It's not possible to run server software on GitHub Actions using regular methods: the worker virtual machine is placed behind Network Address Translation (NAT), which prevents it from receiving direct inbound TCP/UDP connections.

This repository consists of GitHub Actions jobs for OpenVPN and WireGuard VPN servers which traverse NAT, making possible to establish VPN connection to the Actions worker machine directly, without any additional tunnel, third-party service, or port forwarding software.

This is a step-by-step, thoroughly documented practical UDP NAT traversal showcase using GitHub Actions with OpenVPN/WireGuard servers as an example, with only stock software from Ubuntu repositories.