diff --git a/lib/distributed-service/tests/default.nix b/lib/distributed-service/tests/default.nix
index 3ef549646..4ab86e351 100644
--- a/lib/distributed-service/tests/default.nix
+++ b/lib/distributed-service/tests/default.nix
@@ -59,4 +59,269 @@ in
       expr = res.evals ? "self-simple-module";
       expected = true;
     };
+
+  # A module can be imported multiple times
+  # A module can also have multiple instances within the same module
+  # This mean modules must be grouped together, imported once
+  # All instances should be included within one evaluation to make all of them available
+  test_module_grouping =
+    let
+      res = callInventoryAdapter {
+        # Authored module
+        # A minimal module looks like this
+        # It isn't exactly doing anything but it's a valid module that produces an output
+        modules."A" = {
+          _class = "clan.service";
+          manifest = {
+            name = "A-name";
+          };
+
+          perMachine = { }: { };
+        };
+        modules."B" = {
+          _class = "clan.service";
+          manifest = {
+            name = "B-name";
+          };
+
+          perMachine = { }: { };
+        };
+        # User config
+        instances."instance_foo" = {
+          module = {
+            name = "A";
+          };
+        };
+        instances."instance_bar" = {
+          module = {
+            name = "B";
+          };
+        };
+        instances."instance_baz" = {
+          module = {
+            name = "A";
+          };
+        };
+      };
+    in
+    {
+      # Test that the module is mapped into the output
+      # We might change the attribute name in the future
+      expr = lib.mapAttrs (_n: v: builtins.length v) res.grouped;
+      expected = {
+        self-A = 2;
+        self-B = 1;
+      };
+    };
+
+  test_creates_all_instances =
+    let
+      res = callInventoryAdapter {
+        # Authored module
+        # A minimal module looks like this
+        # It isn't exactly doing anything but it's a valid module that produces an output
+        modules."A" = {
+          _class = "clan.service";
+          manifest = {
+            name = "network";
+          };
+
+          perMachine = { }: { };
+        };
+        instances."instance_foo" = {
+          module = {
+            name = "A";
+          };
+        };
+        instances."instance_bar" = {
+          module = {
+            name = "A";
+          };
+        };
+        instances."instance_zaza" = {
+          module = {
+            name = "B";
+          };
+        };
+      };
+    in
+    {
+      # Test that the module is mapped into the output
+      # We might change the attribute name in the future
+      expr = lib.attrNames res.evals.self-A.config.instances;
+      expected = [
+        "instance_bar"
+        "instance_foo"
+      ];
+    };
+
+  # Membership via roles
+  test_add_machines_directly =
+    let
+      res = callInventoryAdapter {
+        # Authored module
+        # A minimal module looks like this
+        # It isn't exactly doing anything but it's a valid module that produces an output
+        modules."A" = {
+          _class = "clan.service";
+          manifest = {
+            name = "network";
+          };
+          # Define a role without special behavior
+          roles.peer = { };
+
+          # perMachine = {}: {};
+        };
+        machines = {
+          jon = { };
+          sara = { };
+          hxi = { };
+        };
+        instances."instance_foo" = {
+          module = {
+            name = "A";
+          };
+          roles.peer.machines.jon = { };
+        };
+        instances."instance_bar" = {
+          module = {
+            name = "A";
+          };
+          roles.peer.machines.sara = { };
+        };
+        instances."instance_zaza" = {
+          module = {
+            name = "B";
+          };
+          roles.peer.tags.all = { };
+        };
+      };
+    in
+    {
+      # Test that the module is mapped into the output
+      # We might change the attribute name in the future
+      expr = lib.attrNames res.evals.self-A.config.result.allMachines;
+      expected = [
+        "jon"
+        "sara"
+      ];
+    };
+
+  # Membership via tags
+  test_add_machines_via_tags =
+    let
+      res = callInventoryAdapter {
+        # Authored module
+        # A minimal module looks like this
+        # It isn't exactly doing anything but it's a valid module that produces an output
+        modules."A" = {
+          _class = "clan.service";
+          manifest = {
+            name = "network";
+          };
+          # Define a role without special behavior
+          roles.peer = { };
+
+          # perMachine = {}: {};
+        };
+        machines = {
+          jon = {
+            tags = [ "foo" ];
+          };
+          sara = {
+            tags = [ "foo" ];
+          };
+          hxi = { };
+        };
+        instances."instance_foo" = {
+          module = {
+            name = "A";
+          };
+          roles.peer.tags.foo = { };
+        };
+        instances."instance_zaza" = {
+          module = {
+            name = "B";
+          };
+          roles.peer.tags.all = { };
+        };
+      };
+    in
+    {
+      # Test that the module is mapped into the output
+      # We might change the attribute name in the future
+      expr = lib.attrNames res.evals.self-A.config.result.allMachines;
+      expected = [
+        "jon"
+        "sara"
+      ];
+    };
+
+  per_machine_args = import ./per_machine_args.nix { inherit lib callInventoryAdapter; };
+  # test_per_machine_receives_instances =
+  #   let
+  #     res = callInventoryAdapter {
+  #       # Authored module
+  #       # A minimal module looks like this
+  #       # It isn't exactly doing anything but it's a valid module that produces an output
+  #       modules."A" = {
+  #         _class = "clan.service";
+  #         manifest = {
+  #           name = "network";
+  #         };
+  #         # Define a role without special behavior
+  #         roles.peer = { };
+
+  #         perMachine =
+  #           { instances, ... }:
+  #           {
+  #             nixosModule = instances;
+  #           };
+  #       };
+  #       machines = {
+  #         jon = { };
+  #         sara = { };
+  #       };
+  #       instances."instance_foo" = {
+  #         module = {
+  #           name = "A";
+  #         };
+  #         roles.peer.machines.jon = { };
+  #       };
+  #       instances."instance_bar" = {
+  #         module = {
+  #           name = "A";
+  #         };
+  #         roles.peer.machines.sara = { };
+  #       };
+  #       instances."instance_zaza" = {
+  #         module = {
+  #           name = "B";
+  #         };
+  #         roles.peer.tags.all = { };
+  #       };
+  #     };
+  #   in
+  #   {
+  #     expr = {
+  #       hasMachineSettings =
+  #         res.evals.self-A.config.result.allMachines.jon.nixosModule. # { {instanceName} :: { roles :: { {roleName} :: { machines :: { {machineName} :: { settings :: {} } } } } } }
+  #         instance_foo.roles.peer.machines.jon ? settings;
+  #       machineSettingsEmpty =
+  #         lib.filterAttrs (n: _v: n != "__functor" ) res.evals.self-A.config.result.allMachines.jon.nixosModule. # { {instanceName} :: { roles :: { {roleName} :: { machines :: { {machineName} :: { settings :: {} } } } } } }
+  #         instance_foo.roles.peer.machines.jon.settings;
+  #       hasRoleSettings =
+  #         res.evals.self-A.config.result.allMachines.jon.nixosModule. # { {instanceName} :: { roles :: { {roleName} :: { machines :: { {machineName} :: { settings :: {} } } } } } }
+  #         instance_foo.roles.peer ? settings;
+  #       roleSettingsEmpty =
+  #         lib.filterAttrs (n: _v: n != "__functor" ) res.evals.self-A.config.result.allMachines.jon.nixosModule. # { {instanceName} :: { roles :: { {roleName} :: { machines :: { {machineName} :: { settings :: {} } } } } } }
+  #         instance_foo.roles.peer.settings;
+  #     };
+  #     expected = {
+  #       hasMachineSettings = true;
+  #       machineSettingsEmpty = {};
+  #       hasRoleSettings = true;
+  #       roleSettingsEmpty = {};
+  #     };
+  #   };
 }
diff --git a/lib/distributed-service/tests/per_machine_args.nix b/lib/distributed-service/tests/per_machine_args.nix
new file mode 100644
index 000000000..ad4784af6
--- /dev/null
+++ b/lib/distributed-service/tests/per_machine_args.nix
@@ -0,0 +1,107 @@
+{ lib, callInventoryAdapter }:
+
+let # Authored module
+  # A minimal module looks like this
+  # It isn't exactly doing anything but it's a valid module that produces an output
+  modules."A" = {
+    _class = "clan.service";
+    manifest = {
+      name = "network";
+    };
+    # Define two roles with unmergeable interfaces
+    # Both define some 'timeout' but with completely different types.
+    roles.peer.interface =
+      { lib, ... }:
+      {
+        options.timeout = lib.mkOption {
+          type = lib.types.str;
+        };
+      };
+    roles.server.interface =
+      { lib, ... }:
+      {
+        options.timeout = lib.mkOption {
+          type = lib.types.submodule;
+        };
+      };
+
+    perMachine =
+      { instances, ... }:
+      {
+        nixosModule = instances;
+      };
+  };
+  machines = {
+    jon = { };
+    sara = { };
+  };
+  res = callInventoryAdapter {
+    inherit modules machines;
+    instances."instance_foo" = {
+      module = {
+        name = "A";
+      };
+      roles.peer.machines.jon = {
+        settings.timeout = lib.mkForce "foo-peer-jon";
+      };
+      roles.peer = {
+        settings.timeout = "foo-peer";
+      };
+    };
+    instances."instance_bar" = {
+      module = {
+        name = "A";
+      };
+      roles.peer.machines.jon = {
+        settings.timeout = "bar-peer-jon";
+      };
+    };
+    instances."instance_zaza" = {
+      module = {
+        name = "B";
+      };
+      roles.peer.tags.all = { };
+    };
+  };
+
+  filterInternals = lib.filterAttrs (n: _v: !lib.hasPrefix "_" n);
+in
+
+{
+
+  # settings should evaluate
+  test_per_machine_receives_instance_settings = {
+    expr = {
+      hasMachineSettings =
+        res.evals.self-A.config.result.allMachines.jon.nixosModule.instance_foo.roles.peer.machines.jon
+        ? settings;
+
+      # settings are specific.
+      # Below we access:
+      # instance = instance_foo
+      # roles = peer
+      # machines = jon
+      specificMachineSettings = filterInternals res.evals.self-A.config.result.allMachines.jon.nixosModule.instance_foo.roles.peer.machines.jon.settings;
+
+      hasRoleSettings =
+        res.evals.self-A.config.result.allMachines.jon.nixosModule.instance_foo.roles.peer ? settings;
+
+      # settings are specific.
+      # Below we access:
+      # instance = instance_foo
+      # roles = peer
+      # machines = *
+      specificRoleSettings = filterInternals res.evals.self-A.config.result.allMachines.jon.nixosModule.instance_foo.roles.peer.settings;
+    };
+    expected = {
+      hasMachineSettings = true;
+      specificMachineSettings = {
+        timeout = "foo-peer-jon";
+      };
+      hasRoleSettings = true;
+      specificRoleSettings = {
+        timeout = "foo-peer";
+      };
+    };
+  };
+}