Most sysadmin love to use Ubuntu’s Uncomplicated firewall because it is available on Ubuntu and it’s very simple. One of the basic usage is to use ufw to NAT the connections from the Internet to the internal server using ufw. From the tutorial:
How do I forward TCP HTTP port # 80 and 443 to an internal server hosted at 192.168.1.100:80 and 192.168.1.100:443 using UFW on Ubuntu Linux server? In this tutorial, you will learn how to forward incoming traffic to your server running ufw on port 80/443 to port 80/443 on another internal server hosted in your LAN/VLAN.