modules/systemd-extras: introduce distributed service interface

modules/systemd-extras/default.nix

@@ -1,5 +1,6 @@
 {
   imports = [
     ./strict-mounts.nix
+    ./distributed.nix
   ];
 }

modules/systemd-extras/distributed.nix

@@ -0,0 +1,23 @@
+{ lib, ... }:
+
+with lib;
+{
+  options.systemd.services = mkOption {
+    type = with types; attrsOf (submodule ({ config, ... }: {
+      options.distributed = {
+        enable = mkEnableOption "distributed mode";
+
+        replicas = mkOption {
+          description = "Maximum number of replicas to run at once.";
+          type = types.int;
+          default = 1;
+        };
+        registerService = mkOption {
+          description = "Consul service to register when this service gets started.";
+          type = with types; nullOr str;
+          default = null;
+        };
+      };
+    }));
+  };
+}