hosts/monitoring-3: validate nixos hash versions

hosts/monitoring-3/nixos-validator.nix

@@ -0,0 +1,27 @@
+{ pkgs, ... }:
+{
+
+  users.users."nixos-validator" = {
+    isSystemUser = true;
+    group = "nixos-validator";
+  };
+
+  users.groups."nixos-validator" = {};
+
+  systemd.services."prometheus-nixos-validator" = {
+    wantedBy = [ "multi-user.target" ];
+    after = [ "network.target" ];
+    serviceConfig = {
+      Restart = "always";
+      PrivateTmp = true;
+      WorkingDirectory = "/tmp";
+      RuntimeDirectory = "prometheus-nixos-validator";
+      User = "nixos-validator";
+      Group = "nixos-validator";
+      ExecStart = ''
+        ${pkgs.nixos-exporter}/bin/nixos-exporter --listen [::]:9153 validator --prometheus-url "http://[::1]:9090" --prometheus-query-tag-template "instance=\"{}.net.clerie.de\"" --hydra-url "https://hydra.clerie.de"
+      '';
+    };
+  };
+
+}