building a nix docker image

docker.nix

with import <nixpkgs> {};

let 
niximage = dockerTools.buildImage {
  name = "nix";
  tag = "1.11.2";
  contents = [ nix cacert bash ];
};
nixpkgs = import /nix/store/xxxxx-nixpkgs.drv;

in
dockerTools.buildImage {
  name = "nix";
  tag = "1.11.2";
  fromImage = niximage;
  runAsRoot = ''
    #!${stdenv.shell}

    set -xe
    ${dockerTools.shadowSetup}
    mkdir -p /home
    useradd -m user
    mkdir /tmp && chmod 777 /tmp
  '';
  
  config = {
    User = "user";
    Env = ["HOME=/home/user" "NIX_PATH=nixpkgs=/nixpkgs" "SSL_CERT_FILE=/etc/ssl/certs/ca-bundle.crt"];
  };
}