Inventory/constraints: add id's to inventory constraints to make them more observable

lib/constraints/interface.nix

@@ -1,9 +1,19 @@
-{ lib, allRoles, ... }:
+{
+  lib,
+  allRoles,
+  moduleName,
+  ...
+}:
 let
   inherit (lib) mkOption types;
   rolesAttrs = builtins.groupBy lib.id allRoles;
 in
 {
+  options.serviceName = mkOption {
+    type = types.str;
+    default = moduleName;
+    readOnly = true;
+  };
   options.roles = lib.mapAttrs (
     _name: _:
     mkOption {
@@ -20,10 +30,6 @@ in
                 type = types.int;
                 default = 0;
               };
-              eq = mkOption {
-                type = types.nullOr types.int;
-                default = null;
-              };
             };
           }
         ];
@@ -31,10 +37,26 @@ in
     }
   ) rolesAttrs;
 
+  options.instances = mkOption {
+    default = { };
+    type = types.submoduleWith {
+      modules = [
+        {
+          options = {
+            max = mkOption {
+              type = types.nullOr types.int;
+              default = null;
+            };
+          };
+        }
+      ];
+    };
+  };
+
   # The resulting assertions
   options.assertions = mkOption {
-    default = [ ];
-    type = types.listOf (
+    default = { };
+    type = types.attrsOf (
       types.submoduleWith {
         modules = [
           {