try add arion example

nixos/arion/arion-compose.nix

@@ -0,0 +1,50 @@
+
+/*
+
+  DISCLAIMER
+
+  This uses a somewhat hidden feature in NixOS, which is the
+  "runner". It's a script that's available on systemd services
+  that lets you run the service independently from systemd.
+  However, it was clearly not intended for public consumption
+  so please use it with care.
+  It does not support all features of systemd so you are on
+  your own if you use it in production.
+
+  One known issue is that the script does not respond to docker's
+  SIGTERM shutdown signal.
+
+ */
+
+{
+  project.name = "nixos-unit";
+  services.webserver = { config, pkgs, ... }: {
+
+    nixos.configuration = {config, lib, options, pkgs, ...}: {
+      boot.isContainer = true;
+      services.nginx = {
+        enable = true;
+        virtualHosts.localhost.root = "${pkgs.nix.doc}/share/doc/nix/manual";
+      } // lib.optionalAttrs (options?services.nginx.stateDir) {
+        # Work around a problem in NixOS 20.03
+        stateDir = "/var/lib/nginx";
+      };
+      system.build.run-nginx = pkgs.writeScript "run-nginx" ''
+        #!${pkgs.bash}/bin/bash
+        PATH='${config.systemd.services.nginx.environment.PATH}'
+        echo nginx:x:${toString config.users.users.nginx.uid}:${toString config.users.groups.nginx.gid}:nginx web server user:/var/empty:/bin/sh >>/etc/passwd
+        echo nginx:x:${toString config.users.groups.nginx.gid}:nginx >>/etc/group
+        echo 'nobody:x:65534:65534:Unprivileged account do not use:/var/empty:/run/current-system/sw/bin/nologin' >>/etc/passwd
+        echo 'nogroup:x:65534:' >>/etc/group
+        mkdir -p /var/log/nginx /run/nginx/ /var/cache/nginx /var/lib/nginx/{,logs,proxy_temp,client_body_temp,fastcgi_temp,scgi_temp,uwsgi_temp} /tmp/nginx_client_body
+        chown nginx /var/log/nginx /run/nginx/ /var/cache/nginx /var/lib/nginx/{,logs,proxy_temp,client_body_temp,fastcgi_temp,scgi_temp,uwsgi_temp} /tmp/nginx_client_body
+        ${config.systemd.services.nginx.runner}
+      '';
+    };
+    service.command = [ config.nixos.build.run-nginx ];
+    service.useHostStore = true;
+    service.ports = [
+      "8000:80" # host:container
+    ];
+  };
+}

nixos/arion/arion-pkgs.nix

@@ -0,0 +1,10 @@
+## This file is the default location for Arion to look for Nixpkgs when
+## bootstrapping a deployment configuration.
+#import ../ {}
+
+# Instead of pinning Nixpkgs, we can opt to use the one in NIX_PATH
+import <nixpkgs> {
+  # We specify the architecture explicitly. Use a Linux remote builder when
+  # calling arion from other platforms.
+  system = "x86_64-linux";
+}