system/nixos/modules/wireguard-client.nix

{ config, lib, pkgs, ... }:

let
  cfg = config.local.wireguard;

  port = 51820;

  serverAddr = (import ../hosts/canigou/data.secret.nix).addr;

  # Run `ip route` to show gateway
  defaultGateway = "192.168.0.1";
in
{
  options.local.wireguard = with lib; {
    enable = mkEnableOption "Enable wireguard vpn";
    ip = mkOption {
      type = types.str;
      description = "10.100.0.<num>/24";
      example = "10.100.0.1/24";
    };
    privateKeyFile = mkOption {
      type = types.str;
    };
  };

  config = lib.mkIf cfg.enable {
    networking.firewall = {
      allowedUDPPorts = [ port ]; # Clients and peers can use the same port, see listenport
    };
    # Enable WireGuard
    networking.wireguard.interfaces = {
      # "wg0" is the network interface name. You can name the interface arbitrarily.
      wg0 = {
        # Determines the IP address and subnet of the client's end of the tunnel interface.
        ips = [ cfg.ip ];
        listenPort = port; # to match firewall allowedUDPPorts (without this wg uses random port numbers)

        # Path to the private key file.
        privateKeyFile = cfg.privateKeyFile;

        # Add a more specific ip route allowing trafgfic to the VPN via the default gateway
        # Source: https://discourse.nixos.org/t/route-all-traffic-through-wireguard-interface/1480/18
        postSetup = "${pkgs.iproute}/bin/ip route add ${serverAddr} via ${defaultGateway}";
        postShutdown = "${pkgs.iproute}/bin/ip route del ${serverAddr} via ${defaultGateway}";

        peers = [
          # For a client configuration, one peer entry for the server will suffice.

          {
            # Public key of the server (not a file path).
            publicKey = "nFqvL30dkKkhOt+fLJ+EJNmp9GjkXVjmpz1WRI1pG0A=";

            # Forward all the traffic via VPN.
            allowedIPs = [ "0.0.0.0/0" ];
            # Or forward only particular subnets
            # allowedIPs = [ "192.168.0.0/24" ];

            # Set this to the server IP and port.
            endpoint = "${serverAddr}:${toString port}";

            # Send keepalives every 25 seconds. Important to keep NAT tables alive.
            persistentKeepalive = 25;

            dynamicEndpointRefreshRestartSeconds = 5;
          }
        ];
      };
    };
  };
}