feat(monitoring): Enable node exporter on almost all nodes

modules/dgn-node-monitoring.nix

@@ -0,0 +1,43 @@
+{ config, lib, ... }:
+let
+  inherit (lib)
+    mkEnableOption
+    mkIf
+    mkOption
+
+    types
+    ;
+  cfg = config.dgn-node-monitoring;
+in
+
+{
+  options.dgn-node-monitoring = {
+    enable = mkEnableOption "DGNum nodes monitoring (needs a valid netbird tunnel)" // {
+      default = true;
+    };
+    port = mkOption {
+      type = types.port;
+      default = 9002;
+      description = lib.mdDoc ''
+        Port to listen on.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    services.prometheus = {
+      exporters = {
+        node = {
+          enable = true;
+          enabledCollectors = [
+            "processes"
+            "systemd"
+          ];
+          inherit (cfg) port;
+          listenAddress = "0.0.0.0";
+        };
+      };
+    };
+    networking.firewall.interfaces.wt0.allowedTCPPorts = [ cfg.port ];
+  };
+}