I'm pursuing the reason behind why routers add security to a domain of a server architecture and front-end HTTP and HTTPS servers.
Architecture: Assume I get a static IP of 100.100.100.100 from an ISP and I set up the following in the server room:
IP -> Server 1 (HTTP/HTTPS) <-LAN-> Switch(Server 2(Web App), Server 3(DB))
For serving all visitors, I close all ports not related to HTTP/HTTPS. So now, if I add a router between IP and server 1, which firewall rules will help me with respect to the security aspects of things? Does it just add another unnecessary level of complexity? Or am I mistaken and missing something huge here?