Resolve dns queries on overlay with the recursive ns

hosts/homeserver/default.nix

@@ -21,6 +21,7 @@
       };
 
       services = {
+        recursive-nameserver.enable = true;
         private-nameserver.enable = true;
 
         syncthing = {

hosts/vps-ns/default.nix

@@ -21,6 +21,7 @@
     };
 
     services = {
+      recursive-nameserver.enable = true;
       private-nameserver.enable = true;
       public-nameserver = {
         enable = true;

modules/nixos/networking/overlay.nix

@@ -63,8 +63,11 @@ in
       default =
         allHosts
         |> lib.attrValues
-        |> lib.filter (host: host.config.custom.services.private-nameserver.enable)
+        |> lib.filter (host: host.config.custom.services.recursive-nameserver.enable)
-        |> lib.map (host: host.config.custom.networking.overlay.address);
+        |> lib.map (
+          host:
+          "${host.config.custom.networking.overlay.address}:${toString host.config.custom.services.recursive-nameserver.port}"
+        );
     };
 
     implementation = lib.mkOption {

modules/nixos/services/nameservers/private.nix

@@ -58,18 +58,24 @@ let
   };
 in
 {
-  options.custom.services.private-nameserver.enable = lib.mkEnableOption "";
+  options.custom.services.private-nameserver = {
+    enable = lib.mkEnableOption "";
+    port = lib.mkOption {
+      type = lib.types.port;
+      default = 5335;
+    };
+  };
 
   config = lib.mkIf cfg.enable {
     services = {
       nsd = {
         enable = true;
-        interfaces = [ netCfg.overlay.interface ];
+        interfaces = [ "${netCfg.overlay.address}@${toString cfg.port}" ];
         zones.${netCfg.overlay.domain}.data = zoneData;
       };
 
       nebula.networks.mesh.firewall.inbound = lib.singleton {
-        port = 53;
+        inherit (cfg) port;
         proto = "any";
         host = "any";
       };

modules/nixos/services/nameservers/public.nix

@@ -66,6 +66,10 @@ in
 {
   options.custom.services.public-nameserver = {
     enable = lib.mkEnableOption "";
+    port = lib.mkOption {
+      type = lib.types.port;
+      default = 53;
+    };
     zones = lib.mkOption {
       type = lib.types.nonEmptyListOf lib.types.nonEmptyStr;
       default = [ ];
@@ -73,14 +77,9 @@ in
   };
 
   config = lib.mkIf cfg.enable {
-    networking.firewall = {
-      allowedTCPPorts = [ 53 ];
-      allowedUDPPorts = [ 53 ];
-    };
-
     services.nsd = {
       enable = true;
-      interfaces = [ netCfg.underlay.interface ];
+      interfaces = [ "${netCfg.underlay.address}@${toString cfg.port}" ];
       zones =
         cfg.zones
         |> lib.map (zone: {
@@ -89,5 +88,10 @@ in
         })
         |> lib.listToAttrs;
     };
+
+    networking.firewall = {
+      allowedTCPPorts = [ cfg.port ];
+      allowedUDPPorts = [ cfg.port ];
+    };
   };
 }

modules/nixos/services/nameservers/recursive.nix

@@ -0,0 +1,70 @@
+{
+  config,
+  lib,
+  allHosts,
+  ...
+}:
+let
+  cfg = config.custom.services.recursive-nameserver;
+  netCfg = config.custom.networking;
+
+  privateNameservers =
+    allHosts
+    |> lib.attrValues
+    |> lib.filter (host: host.config.custom.services.private-nameserver.enable);
+in
+{
+  options.custom.services.recursive-nameserver = {
+    enable = lib.mkEnableOption "";
+    port = lib.mkOption {
+      type = lib.types.port;
+      default = 53;
+    };
+  };
+
+  config = lib.mkIf cfg.enable (
+    lib.mkMerge [
+      {
+        services = {
+          unbound = {
+            enable = true;
+            settings.server = {
+              interface = [ "${netCfg.overlay.address}@${toString cfg.port}" ];
+              access-control = [ "${toString netCfg.overlay.networkCidr} allow" ];
+            };
+          };
+
+          nebula.networks.mesh.firewall.inbound = lib.singleton {
+            inherit (cfg) port;
+            proto = "any";
+            host = "any";
+          };
+        };
+
+        systemd.services.unbound = {
+          requires = [ netCfg.overlay.systemdUnit ];
+          after = [ netCfg.overlay.systemdUnit ];
+        };
+      }
+
+      (lib.mkIf (privateNameservers != [ ]) {
+        services.unbound.settings = {
+          server = {
+            local-zone = ''"${netCfg.overlay.domain}." nodefault'';
+            domain-insecure = netCfg.overlay.domain;
+          };
+
+          stub-zone = lib.singleton {
+            name = netCfg.overlay.domain;
+            stub-addr =
+              privateNameservers
+              |> lib.map (
+                host:
+                "${host.config.custom.networking.overlay.address}@${toString host.config.custom.services.private-nameserver.port}"
+              );
+          };
+        };
+      })
+    ]
+  );
+}

tests/infrastructure/default.nix

@@ -58,7 +58,10 @@
           };
         };
 
-        services.private-nameserver.enable = true;
+        services = {
+          recursive-nameserver.enable = true;
+          private-nameserver.enable = true;
+        };
       };
     };
 
@@ -133,7 +136,7 @@
       client1.wait_for_unit("${client1NetCfg.overlay.systemdUnit}")
       client2.wait_for_unit("${client2NetCfg.overlay.systemdUnit}")
 
-      lighthouse.wait_for_unit("nsd.service")
+      lighthouse.wait_for_unit("unbound.service")
       lighthouse.wait_for_open_port(53, "${lighthouseNetCfg.overlay.address}")
 
       server.wait_for_unit("sshd.service")