Add support for remote Nix builders

hosts/Khanda/default.nix

@@ -39,12 +39,8 @@
 		};
 	};
 
-	# Limit number of simultaneous builds so we have two free cores.
-	# 	5 max jobs * 2 cores each = 10 cores in total.
-	nix.settings = {
-		max-jobs = 2;
-		cores = 10;
-	};
+	# Build remotely
+	nix.distributedBuilds = true;
 
 	# Configure the virtual machine created by nixos-rebuild build-vm
 	virtualisation.vmVariant.virtualisation = {

modules/base/default.nix

@@ -3,6 +3,7 @@
 		./bluetooth.nix
 		./bootloader.nix
 		./network.nix
+		./nix.nix
 		./shell.nix
 		./system.nix
 	];

modules/base/nix.nix

@@ -0,0 +1,42 @@
+# Nix configuration
+{ pkgs, config, lib, inputs, ... }: {
+	nix = {
+		# Use the latest and greatest Nix
+		package = pkgs.nixVersions.unstable;
+
+		settings = {
+			# Enables Flakes
+			experimental-features = [ "nix-command" "flakes" ];
+
+			# Avoid signature verification messages when doing remote builds
+			trusted-users = [ "${config.users.users.aires.name}" ];
+		};
+
+		# Enable periodic nix store optimization
+		optimise.automatic = true;
+
+		# Configure NixOS to use the same software channel as Flakes
+		registry = lib.mapAttrs (_: value: { flake = value; }) inputs;
+		nixPath = lib.mapAttrsToList (key: value: "${key}=${value.to.path}") config.nix.registry;
+
+		# Configure remote build machines (mainly Haven)
+		# To enable remote builds for a specific host, add `nix.distributedBuilds = true;` to its config
+		buildMachines = [{ 
+			hostName = "haven";
+			systems = [
+				"x86_64-linux"
+				"aarch64-linux"
+			];
+			protocol = "ssh-ng";
+			supportedFeatures = [
+				"nixos-test"
+				"kvm"
+			];
+		}];
+
+		# When using a builder, use its package store
+		extraOptions = ''
+			builders-use-substitutes = true
+		'';
+	};
+}

modules/base/system.nix

@@ -69,27 +69,6 @@ with lib;
 			};
 		};
 
-		# Configure nix
-		nix = {
-			# Use the latest and greatest Nix
-			package = pkgs.nixVersions.unstable;
-
-			settings = {
-				# Enables Flakes
-				experimental-features = [ "nix-command" "flakes" ];
-
-				# Avoid signature verification messages when doing remote builds
-				trusted-users = [ "${config.users.users.aires.name}" ];
-			};
-
-			# Enable periodic nix store optimization
-			optimise.automatic = true;
-
-			# Configure NixOS to use the same software channel as Flakes
-			registry = lib.mapAttrs (_: value: { flake = value; }) inputs;
-			nixPath = lib.mapAttrsToList (key: value: "${key}=${value.to.path}") config.nix.registry;
-		};
-
 		# Set up base apps
 		programs = {
 			direnv.enable = true;