Add monitoring in the bay node

m/bay/configuration.nix

@@ -3,6 +3,7 @@
 {
   imports = [
     ../common/main.nix
+    ./monitoring.nix
   ];
 
   # Select the this using the ID to avoid mismatches

m/bay/monitoring.nix

@@ -0,0 +1,25 @@
+{ config, lib, ... }:
+
+{
+  # We need access to the devices to monitor the disk space
+  systemd.services.prometheus-node-exporter.serviceConfig.PrivateDevices = lib.mkForce false;
+  systemd.services.prometheus-node-exporter.serviceConfig.ProtectHome = lib.mkForce "read-only";
+
+  # Required to allow the smartctl exporter to read the nvme0 character device,
+  # see the commit message on:
+  # https://github.com/NixOS/nixpkgs/commit/12c26aca1fd55ab99f831bedc865a626eee39f80
+  services.udev.extraRules = ''
+    SUBSYSTEM=="nvme", KERNEL=="nvme[0-9]*", GROUP="disk"
+  '';
+
+  services.prometheus = {
+    exporters = {
+      node = {
+        enable = true;
+        enabledCollectors = [ "systemd" ];
+        port = 9002;
+      };
+      smartctl.enable = true;
+    };
+  };
+}