nixos/coredns: init (#54931)

nixos/modules/module-list.nix

@@ -528,6 +528,7 @@
   ./services/networking/cntlm.nix
   ./services/networking/connman.nix
   ./services/networking/consul.nix
+  ./services/networking/coredns.nix
   ./services/networking/coturn.nix
   ./services/networking/dante.nix
   ./services/networking/ddclient.nix

nixos/modules/services/networking/coredns.nix

@@ -0,0 +1,50 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.coredns;
+  configFile = pkgs.writeText "Corefile" cfg.config;
+in {
+  options.services.coredns = {
+    enable = mkEnableOption "Coredns dns server";
+
+    config = mkOption {
+      default = "";
+      example = ''
+        . {
+          whoami
+        }
+      '';
+      type = types.lines;
+      description = "Verbatim Corefile to use. See <link xlink:href=\"https://coredns.io/manual/toc/#configuration\"/> for details.";
+    };
+
+    package = mkOption {
+      default = pkgs.coredns;
+      defaultText = "pkgs.coredns";
+      type = types.package;
+      description = "Coredns package to use.";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    systemd.services.coredns = {
+      description = "Coredns dns server";
+      after = [ "network.target" ];
+      wantedBy = [ "multi-user.target" ];
+      serviceConfig = {
+        PermissionsStartOnly = true;
+        LimitNPROC = 512;
+        LimitNOFILE = 1048576;
+        CapabilityBoundingSet = "cap_net_bind_service";
+        AmbientCapabilities = "cap_net_bind_service";
+        NoNewPrivileges = true;
+        DynamicUser = true;
+        ExecStart = "${getBin cfg.package}/bin/coredns -conf=${configFile}";
+        ExecReload = "${pkgs.coreutils}/bin/kill -SIGUSR1 $MAINPID";
+        Restart = "on-failure";
+      };
+    };
+  };
+}