monitoring: add nixos-exporter to monitoring01

Enable the nixos-exporter prometheus exporter with flake collector
to track NixOS generation metrics and flake revision status.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

flake.lock

@@ -42,6 +42,26 @@
         "url": "https://git.t-juice.club/torjus/labmon"
       }
     },
+    "nixos-exporter": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs-unstable"
+        ]
+      },
+      "locked": {
+        "lastModified": 1770415085,
+        "narHash": "sha256-8XhzLc9wIoxL/OwKmX9LxpYCbmz3iMuuAX/4ILnw2TQ=",
+        "ref": "refs/heads/master",
+        "rev": "858e047bff6224c90ff5d033f8adbbba01036029",
+        "revCount": 2,
+        "type": "git",
+        "url": "https://git.t-juice.club/torjus/nixos-exporter"
+      },
+      "original": {
+        "type": "git",
+        "url": "https://git.t-juice.club/torjus/nixos-exporter"
+      }
+    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1770136044,
@@ -78,6 +98,7 @@
       "inputs": {
         "alerttonotify": "alerttonotify",
         "labmon": "labmon",
+        "nixos-exporter": "nixos-exporter",
         "nixpkgs": "nixpkgs",
         "nixpkgs-unstable": "nixpkgs-unstable",
         "sops-nix": "sops-nix"

flake.nix

@@ -17,6 +17,10 @@
       url = "git+https://git.t-juice.club/torjus/labmon?ref=master";
       inputs.nixpkgs.follows = "nixpkgs-unstable";
     };
+    nixos-exporter = {
+      url = "git+https://git.t-juice.club/torjus/nixos-exporter";
+      inputs.nixpkgs.follows = "nixpkgs-unstable";
+    };
   };
 
   outputs =
@@ -27,6 +31,7 @@
       sops-nix,
       alerttonotify,
       labmon,
+      nixos-exporter,
       ...
     }@inputs:
     let
@@ -180,6 +185,7 @@
             ./hosts/monitoring01
             sops-nix.nixosModules.sops
             labmon.nixosModules.labmon
+            nixos-exporter.nixosModules.default
           ];
         };
         jelly01 = nixpkgs.lib.nixosSystem {

hosts/monitoring01/configuration.nix

@@ -99,6 +99,23 @@
     ];
   };
 
+  # NixOS metrics exporter
+  services.prometheus.exporters.nixos = {
+    enable = true;
+    flake = {
+      enable = true;
+      url = "git+https://git.t-juice.club/torjus/nixos-servers.git";
+    };
+  };
+
+  # Register nixos-exporter as a Prometheus scrape target
+  homelab.monitoring.scrapeTargets = [
+    {
+      job_name = "nixos-exporter";
+      port = 9971;
+    }
+  ];
+
   labmon = {
     enable = true;