quilkin VS matchbox

Quilkin should work for this. Set up one client on your VPS, then set up a second client on a host somewhere inside your network. Connect both instances together and have the host on your network forward traffic to the 27016 endpoint

The firewall would need to be able to handle all the DDoS traffic as well, since your current idea would still pass the game server's IP back to a client. This is doable if you're hosting on a cloud provider and let their firewalls filter the traffic before hitting the game server.

Embark Studios recently open sourced (in alpha) a UDP proxy[1] designed for games that lets you implement a load balancing layer. This allows you to remove servers in the load balancing layer in the event that it comes under attack, allowing the game server to stay up and only having to disconnect a portion of players connected to the attacked loadbalancer. Having a proxy layer is also how Steam protects game servers using the Steam Datagram Relay[2].

[1]: https://github.com/googleforgames/quilkin

The “collaboration” feature is achieved thanks to matchbox crate, a peer-to-peer WebRTC networking library.

Consider using https://github.com/johanhelsing/matchbox to help with the WebRTC problem, I hear good things about it

https://github.com/johanhelsing/matchbox

Even then, you'd cover only some very specific use-cases of multiplayer game-making.

That's the approach taken by the matchbox project, and it's done pretty well.

In theory, it should also be possible to support browser-native crossplay that way. I did some work on supporting that, but I'm currently stuck on an issue with webrtc-rs.