Crafting a Scalable and Modern Flake Structure for Managing Multiple NixOS Server Configurations:

I want to have a single flake for managing multiple server configuration for nixos so that i can rebuild with the corresponding server name $".$server$1"$ for example. Show me a modern and elegant example. Make sure it's complete and scalable in case I have $10$ clusters. Do not use flake$-$utils and account for having multiple inputs such as latest stable channel and nixpkgs$-$unstable and nixos$-$unstable. Show me the ideal structure.

Do NOT use AI for this question. Provide an output image to show that your code is properly working. Thank you!