nix build .#hydraJobs.system
You will need to be on an aarch64-linux machine or have an aarch64-linux builder configured.
You can use nix-netboot-serve to provide netboot for the resulting configuration.
(TODO: this isn't implemented yet) The production machine boots via the build on hydra.nixos.org using netboot.nixos.org, which is also running nix-netboot-serve.