create a module for round-robin

modules/round-robin/default.nix

@@ -0,0 +1,27 @@
+## Round Robin
+##
+## Given a list of services, run each in turn until it exits, then
+## runs the next.
+
+
+{ lib, pkgs, config, ...}:
+let
+  inherit (lib) mkOption types;
+  inherit (pkgs) liminix;
+  inherit (pkgs.liminix.services) longrun;
+in {
+  options = {
+    system.service.round-robin = mkOption {
+      description = "run services one at a time and failover to next";
+      type = liminix.lib.types.serviceDefn;
+    };
+  };
+  config.system.service.round-robin = config.system.callService ./service.nix {
+    services = mkOption {
+      type = types.listOf  liminix.lib.types.service;
+    };
+    name =  mkOption {
+      type = types.str;
+    };
+  };
+}