add basic darwinModules

enable nix-daemon

darwin/common/default.nix

@@ -0,0 +1,8 @@
+{
+
+  imports = [
+    ./flake.nix
+    ./nix.nix
+    ./openssh.nix
+  ];
+}

darwin/common/flake.nix

@@ -0,0 +1,42 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.srvos;
+in
+{
+  options.srvos = {
+    flake = lib.mkOption {
+      # FIXME what is the type of a flake?
+      type = lib.types.nullOr lib.types.raw;
+      default = null;
+      description = lib.mdDoc ''
+        Flake that contains the nixos configuration.
+      '';
+    };
+  };
+  config = lib.mkIf (cfg.flake != null) {
+    services.telegraf.extraConfig.inputs.file =
+      let
+        inputsWithDate = lib.filterAttrs (_: input: input ? lastModified) cfg.flake.inputs;
+        flakeAttrs = input: (lib.mapAttrsToList (n: v: ''${n}="${v}"'')
+          (lib.filterAttrs (_: v: (builtins.typeOf v) == "string") input));
+        lastModified = name: input: ''
+          flake_input_last_modified{input="${name}",${lib.concatStringsSep "," (flakeAttrs input)}} ${toString input.lastModified}'';
+
+        # avoid adding store path references on flakes which me not need at runtime.
+        promText = builtins.unsafeDiscardStringContext ''
+          # HELP flake_registry_last_modified Last modification date of flake input in unixtime
+          # TYPE flake_input_last_modified gauge
+          ${lib.concatStringsSep "\n" (lib.mapAttrsToList lastModified inputsWithDate)}
+        '';
+      in
+      [
+        {
+          data_format = "prometheus";
+          files = [
+            (pkgs.writeText "flake-inputs.prom" promText)
+          ];
+        }
+      ];
+  };
+}

darwin/common/nix.nix

@@ -0,0 +1,26 @@
+{ lib, config, ... }:
+{
+  services.nix-daemon.enable = true;
+
+  # Fallback quickly if substituters are not available.
+  nix.settings.connect-timeout = 5;
+
+  # Enable flakes
+  nix.settings.experimental-features = [
+    "nix-command"
+    "flakes"
+  ] ++ lib.optional (lib.versionOlder (lib.versions.majorMinor config.nix.package.version) "2.22")
+    "repl-flake";
+
+  # The default at 10 is rarely enough.
+  nix.settings.log-lines = lib.mkDefault 25;
+
+  # Avoid disk full issues
+  nix.settings.max-free = lib.mkDefault (3000 * 1024 * 1024);
+  nix.settings.min-free = lib.mkDefault (512 * 1024 * 1024);
+
+  # Avoid copying unnecessary stuff over SSH
+  nix.settings.builders-use-substitutes = true;
+
+  nix.daemonIOLowPriority = lib.mkDefault true;
+}

darwin/common/openssh.nix

@@ -0,0 +1,17 @@
+# Better defaults for OpenSSH
+{ lib, ... }:
+{
+  environment.etc."ssh/sshd_config.d/102-srvos.conf".text = ''
+    X11Forwarding no
+    KbdInteractiveAuthentication no
+    PasswordAuthentication no
+    UseDns no
+    # unbind gnupg sockets if they exists
+    StreamLocalBindUnlink yes
+    
+    # Use key exchange algorithms recommended by `nixpkgs#ssh-audit`
+    KexAlgorithms curve25519-sha256,curve25519-sha256@libssh.org,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,sntrup761x25519-sha512@openssh.com
+  '';
+  # Only allow system-level authorized_keys to avoid injections.
+  services.openssh.authorizedKeysFiles = lib.mkForce [ "/etc/ssh/authorized_keys.d/%u" ];
+}

darwin/default.nix

@@ -0,0 +1,7 @@
+let
+  exposeModules = import ../lib/exposeModules.nix;
+in
+exposeModules ./. [
+  ./common
+  ./mixins/telegraf.nix
+]

darwin/mixins/telegraf.nix

@@ -0,0 +1,22 @@
+{ lib, inputs, pkgs, ... }:
+{
+  services.telegraf = {
+    enable = true;
+    extraConfig = {
+      agent.interval = "60s";
+      inputs = {
+        smart.path_smartctl = "${pkgs.smartmontools}/bin/smartctl";
+        system = { };
+        mem = { };
+        swap = { };
+        disk.tagdrop.fstype = [ "ramfs" ];
+        diskio = { };
+        internal = { };
+      };
+      outputs.prometheus_client = {
+        listen = ":9273";
+        metric_version = 2;
+      };
+    };
+  };
+}

flake.nix

@@ -94,8 +94,10 @@
 
       # generates future flake outputs: `modules.<kind>.<module-name>`
       flake.modules.nixos = import ./nixos;
+      flake.modules.darwin = import ./darwin;
 
       # compat to current schema: `nixosModules` / `darwinModules`
       flake.nixosModules = self.modules.nixos;
+      flake.darwinModules = self.modules.darwin;
     };
 }