configuration.nix

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

{
  boot.kernel.sysctl."net.ipv4.ip_forward" = 1;

  networking.nat.enable = true;
  networking.nat.internalInterfaces = ["ve-+"];
  networking.nat.externalInterface = "enp0s31f6";

  containers.foo.config =
    { config, pkgs, ... }:
    {
      systemd.services.foo = {
        description = "test service bar";
        wantedBy = [ "multi-user.target" ];
        serviceConfig.Type = "oneshot";
        serviceConfig.ExecStart = "${pkgs.coreutils}/bin/true";
      };
    };
}