A demo "Portable Service" for a shell program built with nix - https://systemd.io/PORTABLE_SERVICES/

default.nix

{ pkgs ? import <nixpkgs> { } }:

let
  demo-program = pkgs.writeShellScriptBin "helloWorld" "while sleep 3; do echo Hello World; done";
  demo-service = pkgs.substituteAll {
    name = "demo.service";
    src = ./demo.service.in;
    demoExe = "${demo-program}/bin/helloWorld";
  };
  demo-socket = pkgs.concatText "demo.socket" [ ./demo.socket ];

in

pkgs.portableService {
  pname = "demo";
  version = "1.0";
  description = ''A demo "Portable Service" for a shell program built with nix'';
  homepage = "https://gist.github.com/gdamjan/9f3e4a4016459d3e12f576ec0813c785";

  units = [ demo-service demo-socket ];

  # let's assume a legacy app will need these at the exact locations
  symlinks = [
    { object = "${pkgs.cacert}/etc/ssl"; symlink = "/etc/ssl"; }
    { object = "${pkgs.bash}/bin/bash"; symlink = "/bin/sh"; }
  ];
}

demo.service.in

[Unit]
Description=demo service
Requires=demo.socket
After=demo.socket

[Service]
Type=simple
ExecStart=@demoExe@
Restart=always

[Install]
WantedBy=multi-user.target
Also=demo.socket

demo.socket

[Unit]
Description=demo socket

[Socket]
ListenStream=/run/demo.sock
SocketMode=0666

[Install]
WantedBy=sockets.target

If you don't run Nix, you can play with this by using podman (or docker):

git clone https://gist.github.com/gdamjan/9f3e4a4016459d3e12f576ec0813c785.git demo-portable-service-nix

# run an interactive container
podman run -ti --rm \
  -v $PWD/demo-portable-service-nix/:/work \
  -e NIX_PATH=nixpkgs=channel:nixos-unstable \
  nixos/nix:latest

# inside the container:
nix-build /work/default.nix
ls result/
sha256sum result/demo_1.0.raw

you should get 93e80c095771dd2e2c45a5755d037ae27e0e15025b41e2c0ba7d08b49bf14181 result/demo_1.0.raw

then, the built image can be run on any Linux with systemd>=240:

sudo portablectl attach --now --runtime $PWD/demo_1.0.raw

(moving the image from one place to another is outside the scope of this gist 🙂)

pkgs.portableService was implemented in NixOS/nixpkgs#161278 and should become available in NixOS 22.11 (in the meanwhile it's available in the nixos-unstable channel)