Separate enabling distributed build vs substituters.

nix/configuration/hosts/family_disks/distributed_build.nix

@@ -4,13 +4,15 @@
   config = {
     me.distributed_build.enable = true;
     me.distributed_build.machines.quark = {
-      enable = false;
+      enable_build = false;
+      enable_substituter = false;
       additional_config = {
         speedFactor = 2;
       };
     };
     me.distributed_build.machines.hydra = {
-      enable = true;
+      enable_build = false;
+      enable_substituter = true;
       additional_config = {
         speedFactor = 2;
       };

nix/configuration/hosts/i_only_boot_zfs/distributed_build.nix

@@ -4,10 +4,19 @@
   config = {
     me.distributed_build.enable = true;
     me.distributed_build.machines.quark = {
-      enable = true;
+      enable_build = false;
+      enable_substituter = false;
       additional_config = {
         speedFactor = 2;
       };
     };
+    me.distributed_build.machines.hydra = {
+      enable_build = false;
+      enable_substituter = true;
+      additional_config = {
+        speedFactor = 2;
+      };
+      substituter_url = "ssh-ng://nixworker@ns1.fizz.buzz:65122?compress=true&ssh-key=/persist/manual/ssh/root/keys/id_ed25519&remote-store=local?root=/.disk/root";
+    };
   };
 }

nix/configuration/hosts/odo/distributed_build.nix

@@ -4,13 +4,15 @@
   config = {
     me.distributed_build.enable = true;
     me.distributed_build.machines.quark = {
-      enable = false;
+      enable_build = false;
+      enable_substituter = false;
       additional_config = {
         speedFactor = 2;
       };
     };
     me.distributed_build.machines.hydra = {
-      enable = true;
+      enable_build = false;
+      enable_substituter = true;
       additional_config = {
         speedFactor = 2;
       };

nix/configuration/hosts/odowork/distributed_build.nix

@@ -4,13 +4,15 @@
   config = {
     me.distributed_build.enable = true;
     me.distributed_build.machines.quark = {
-      enable = false;
+      enable_build = false;
+      enable_substituter = false;
       additional_config = {
         speedFactor = 2;
       };
     };
     me.distributed_build.machines.hydra = {
-      enable = true;
+      enable_build = false;
+      enable_substituter = true;
       additional_config = {
         speedFactor = 2;
       };

nix/configuration/hosts/quark/distributed_build.nix

@@ -3,8 +3,16 @@
 
   config = {
     me.distributed_build.enable = true;
+    me.distributed_build.machines.quark = {
+      enable_build = false;
+      enable_substituter = false;
+      additional_config = {
+        speedFactor = 2;
+      };
+    };
     me.distributed_build.machines.hydra = {
-      enable = true;
+      enable_build = false;
+      enable_substituter = true;
       additional_config = {
         speedFactor = 2;
       };

nix/configuration/hosts/recovery/distributed_build.nix

@@ -4,10 +4,19 @@
   config = {
     me.distributed_build.enable = true;
     me.distributed_build.machines.quark = {
-      enable = true;
+      enable_build = false;
+      enable_substituter = false;
       additional_config = {
         speedFactor = 2;
       };
     };
+    me.distributed_build.machines.hydra = {
+      enable_build = false;
+      enable_substituter = true;
+      additional_config = {
+        speedFactor = 2;
+      };
+      substituter_url = "ssh-ng://nixworker@ns1.fizz.buzz:65122?compress=true&ssh-key=/persist/manual/ssh/root/keys/id_ed25519&remote-store=local?root=/.disk/root";
+    };
   };
 }

nix/configuration/roles/distributed_build/default.nix

@@ -10,7 +10,14 @@
 
 let
   make_machine_config = name: {
-    enable = lib.mkOption {
+    enable_build = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      example = true;
+      description = "Whether we want to use the ${name} machine during distributed builds.";
+    };
+
+    enable_substituter = lib.mkOption {
       type = lib.types.bool;
       default = false;
       example = true;
@@ -59,11 +66,30 @@ let
       hostName = lib.mkForce "hydra?remote-store=local?root=/.disk/root";
     };
   };
+  build_machine_list = (
+    map (
+      hostname:
+      (lib.mkIf config.me.distributed_build.machines."${hostname}".enable_build (
+        lib.mkMerge [
+          {
+            hostName = hostname;
+            sshUser = "nixworker";
+            sshKey = "/persist/manual/ssh/root/keys/id_ed25519";
+            maxJobs = 1;
+            supportedFeatures = all_nixos_configs."${hostname}".config.me.optimizations.system_features;
+            protocol = "ssh-ng";
+          }
+          static_host_configs."${hostname}"
+          config.me.distributed_build.machines."${hostname}".additional_config
+        ]
+      ))
+    ) (builtins.attrNames all_nixos_configs)
+  );
   substituters_list = (
     map (
       hostname:
       (lib.mkIf (
-        config.me.distributed_build.machines."${hostname}".enable
+        config.me.distributed_build.machines."${hostname}".enable_substituter
         && config.me.distributed_build.machines."${hostname}".substituter_url != null
       ) (config.me.distributed_build.machines."${hostname}".substituter_url))
     ) (builtins.attrNames all_nixos_configs)
@@ -112,25 +138,7 @@ in
         ];
       }
       {
-        nix.buildMachines = (
+        nix.buildMachines = build_machine_list;
-          map (
-            hostname:
-            (lib.mkIf config.me.distributed_build.machines."${hostname}".enable (
-              lib.mkMerge [
-                {
-                  hostName = hostname;
-                  sshUser = "nixworker";
-                  sshKey = "/persist/manual/ssh/root/keys/id_ed25519";
-                  maxJobs = 1;
-                  supportedFeatures = all_nixos_configs."${hostname}".config.me.optimizations.system_features;
-                  protocol = "ssh-ng";
-                }
-                static_host_configs."${hostname}"
-                config.me.distributed_build.machines."${hostname}".additional_config
-              ]
-            ))
-          ) (builtins.attrNames all_nixos_configs)
-        );
       }
       (lib.mkIf has_any_substituters {
         nix.settings.substitute = lib.mkForce true;