Start a hydra role.

nix/configuration/configuration.nix

@@ -70,6 +70,7 @@
     ./roles/gcloud
     ./roles/steam_run_free
     ./roles/pcsx2
+    ./roles/hydra
   ];
 
   nix.settings.experimental-features = [

nix/configuration/hosts/hydra/default.nix

@@ -43,6 +43,7 @@
 
   me.emacs_flavor = "plainmacs";
   me.graphical = false;
+  me.hydra.enable = false;
   me.vm_disk.enable = true;
   me.wireguard.activated = [ ];
   me.wireguard.deactivated = [ ];

nix/configuration/roles/hydra/default.nix

@@ -0,0 +1,50 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+{
+  imports = [ ];
+
+  options.me = {
+    hydra.enable = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      example = true;
+      description = "Whether we want to install hydra.";
+    };
+  };
+
+  config = lib.mkIf config.me.hydra.enable (
+    lib.mkMerge [
+      {
+        services.hydra = {
+          enable = true;
+          hydraURL = "http://localhost:3000"; # externally visible URL
+          notificationSender = "hydra@localhost"; # e-mail of Hydra service
+          # a standalone Hydra will require you to unset the buildMachinesFiles list to avoid using a nonexistant /etc/nix/machines
+          buildMachinesFiles = [ ];
+          # you will probably also want, otherwise *everything* will be built from scratch
+          useSubstitutes = true;
+        };
+
+        # nix.buildMachines = [
+        #   {
+        #     hostName = "localhost";
+        #     protocol = null;
+        #     system = "x86_64-linux";
+        #     supportedFeatures = [
+        #       "kvm"
+        #       "nixos-test"
+        #       "big-parallel"
+        #       "benchmark"
+        #     ];
+        #     maxJobs = 8;
+        #   }
+        # ];
+      }
+    ]
+  );
+}