For the very first time i tried to selfhost a static site (lighttpd + duckdns) but I’ve failed… Is it even possible to selfhost a static site from “router 2” while i’m behind two routers? “Router 1” is from ISP and i have no possibility to change any settings except subnet, standard gateway, dhcp on/off and DMZ. -> no port forwarding. "Router 2 is Asus with port-forwarding available and i’m using an OpenVPN configuration on it (if that matters). DuckDNS could see the external ip from R2, but i couldn’t access it.
You want DMZ. I have the same setup. DMZ will make router 1 consider router 2 to be WAN and not behind firewall.