modules/nixos: add cgroups and exporter

hosts/build03/default.nix

@@ -7,6 +7,7 @@
     inputs.self.nixosModules.buildbot
     inputs.self.nixosModules.builder
     inputs.self.nixosModules.ci-builder
+    inputs.self.nixosModules.cgroups
     inputs.self.nixosModules.hercules-ci
     inputs.self.nixosModules.watch-store
     ./builders.nix

hosts/build04/default.nix

@@ -5,6 +5,7 @@
     inputs.self.nixosModules.disko-zfs
     inputs.self.nixosModules.builder
     inputs.self.nixosModules.ci-builder
+    inputs.self.nixosModules.cgroups
     inputs.self.nixosModules.hercules-ci
     inputs.self.nixosModules.remote-builder
   ];

modules/nixos/cgroups.nix

@@ -0,0 +1,31 @@
+{
+  config,
+  inputs,
+  pkgs,
+  ...
+}:
+{
+  imports = [
+    inputs.cgroup-exporter.nixosModules.default
+  ];
+
+  services.prometheus.exporters.cgroup.enable = true;
+
+  services.telegraf.extraConfig.inputs.prometheus.urls = [
+    "http://localhost:${toString config.services.prometheus.exporters.cgroup.port}/metrics"
+  ];
+
+  nix = {
+    package = pkgs.nixVersions.nix_2_25;
+
+    settings = {
+      experimental-features = [
+        "auto-allocate-uids"
+        "cgroups"
+      ];
+
+      auto-allocate-uids = true;
+      use-cgroups = true;
+    };
+  };
+}