feat: distributed builds

modules/common/nix.nix

@@ -1,4 +1,9 @@
-{ pkgs, lib, ...}: {
+{ config, pkgs, lib, ...}: let
+  subs = [
+    "https://cache.thegeneralist01.com/"
+    "https://cache.nixos.org/"
+  ];
+in {
   # todo: gc
   environment.systemPackages = with pkgs; [
     nh
@@ -11,15 +16,28 @@
       "pipe-operators"
     ];
 
-    extra-substituters = [
-      "https://cache.thegeneralist01.com/"
-    ];
+    extra-substituters = subs;
+    trusted-substituters = subs;
 
     extra-trusted-public-keys = [
-      "etc.thegeneralist01.com:BIhIf7HJ5xjFX+2e0WrGDQ4LdHeEEyQrtWBB1li2Ve8="
+      "cache.thegeneralist01.com:jkKcenR877r7fQuWq6cr0JKv2piqBWmYLAYsYsSJnT4="
     ];
+
+    trusted-users = [ "root" "@build" "@wheel" ];
+
+    builders-use-substitutes = true;
   };
 
+  nix.distributedBuilds = true;
+  nix.buildMachines     = if (config.networking.hostName != "thegeneralist-central") then [{
+    hostName            = "thegeneralist-central";
+    maxJobs             = 20;
+    protocol            = "ssh-ng";
+    sshUser             = "build";
+    supportedFeatures   = [ "benchmark" "big-parallel" "kvm" "nixos-test" ];
+    system              = "aarch64-linux";
+  }] else [];
+
   home-manager.sharedModules  = [{
     programs.nh = {
       enable = true;