fix: use name of interface instead of relying on idx

src/maasserver/models/bmc.py

@@ -1088,8 +1088,10 @@ def _assign_interfaces(
     ):
         # Enumerating the LabeledConstraintMap of interfaces will yield the
         # name of each interface, in the same order that they will exist
-        # on the hypervisor. (This is a fortunate coincidence, since
-        # dictionaries in Python 3.6+ preserve insertion order.)
+        # on the hypervisor for virsh. (This is a fortunate coincidence,
+        # since dictionaries in Python 3.6+ preserve insertion order.)
+        # For lxd this is not the case, as there is an API boundary in the
+        # middle that returns reordered interfaces.
         if interface_constraints is not None:
             interface_names = [
                 get_ifname_for_label(label) for label in interface_constraints
@@ -1107,8 +1109,16 @@ def _assign_interfaces(
         # configuration.
         created_interfaces = []
         for idx, discovered_nic in enumerate(discovered_machine.interfaces):
+            # For the scenario of lxd, it returns the interfaces ordered
+            # alphabetically likely due to it being written in Go. So we need
+            # to properly match the correct name here instead of relying on
+            # order.
+            # When coming from virsh, the interfaces do not have a meaningful
+            # name. So we fall back to the previous behavior (which might
+            # be even correct in that scenario.)
+            name = discovered_nic.name or interface_names[idx]
             interface = self._create_interface(
-                discovered_nic, machine, name=interface_names[idx]
+                discovered_nic, machine, name=name
             )
             created_interfaces.append(interface)
             if discovered_nic.boot:

src/maasserver/models/tests/test_bmc.py

@@ -1599,6 +1599,67 @@ def test_create_machine_sets_interface_names_using_constraint_labels(self):
             ),
         )
 
+    def test_create_machine_uses_discovered_interface_name_when_out_of_order(
+        self,
+    ):
+        interfaces = [
+            self.make_discovered_interface(),
+            self.make_discovered_interface(),
+            self.make_discovered_interface(),
+        ]
+        interfaces[0].boot = True
+
+        # Adding names out of alphabetical order, as a previous
+        # bug was inadvertendly reordering things alphabetically.
+        interfaces[0].name = "maas1"
+        interfaces[1].name = "maas0"
+        interfaces[2].name = "maas2"
+
+        mac_to_expected_name = {
+            iface.mac_address: iface.name for iface in interfaces
+        }
+        discovered_machine = self.make_discovered_machine(
+            interfaces=interfaces
+        )
+
+        self.patch(Machine, "set_default_storage_layout")
+        self.patch(Machine, "set_initial_networking_configuration")
+        self.patch(Machine, "start_commissioning")
+
+        fabric = factory.make_Fabric()
+        vlan = factory.make_VLAN(
+            fabric=fabric,
+            dhcp_on=True,
+            primary_rack=factory.make_RackController(),
+        )
+        vlan2 = factory.make_VLAN(
+            fabric=fabric,
+            dhcp_on=False,
+            primary_rack=factory.make_RackController(),
+        )
+        vlan3 = factory.make_VLAN(
+            fabric=fabric,
+            dhcp_on=False,
+            primary_rack=factory.make_RackController(),
+        )
+
+        pod = factory.make_Pod()
+        machine = pod.create_machine(
+            discovered_machine,
+            factory.make_User(),
+            interfaces=LabeledConstraintMap(
+                "maas0:vlan=id:%d;maas1:vlan=id:%d;maas2:vlan=id:%d"
+                % (vlan.id, vlan2.id, vlan3.id)
+            ),
+        )
+        # Each created interface must keep the name reported by the
+        # driver (matched by MAC address), regardless of the position it
+        # occupied in the discovered interfaces list.
+        for interface in machine.current_config.interface_set.all():
+            self.assertEqual(
+                mac_to_expected_name[interface.mac_address], interface.name
+            )
+
     def test_create_machine_allocates_requested_ip_addresses(self):
         discovered_machine = self.make_discovered_machine()
         self.patch(Machine, "set_default_storage_layout")

src/provisioningserver/drivers/pod/__init__.py

@@ -180,6 +180,7 @@ class DiscoveredMachineInterface:
     attach_name = attr.ib(
         converter=converter_obj(str, optional=True), default=None
     )
+    name = attr.ib(converter=converter_obj(str, optional=True), default=None)
 
 
 @attr.s

src/provisioningserver/drivers/pod/lxd.py

@@ -728,6 +728,7 @@ def _get_discovered_interface(name, device, boot):
                 boot=boot,
                 attach_type=attach_type,
                 attach_name=attach_name,
+                name=name,
             )
 
         extra_block_devices = 0

src/provisioningserver/drivers/pod/tests/test_lxd.py

@@ -995,6 +995,7 @@ def test_get_discovered_machine(self):
                 boot=True,
                 attach_type=InterfaceAttachType.BRIDGE,
                 attach_name="lxdbr0",
+                name="eth0",
             ),
         )
         self.assertEqual(
@@ -1006,6 +1007,7 @@ def test_get_discovered_machine(self):
                 boot=False,
                 attach_type=InterfaceAttachType.BRIDGE,
                 attach_name="br1",
+                name="eth1",
             ),
         )
         self.assertEqual(
@@ -1017,6 +1019,7 @@ def test_get_discovered_machine(self):
                 boot=False,
                 attach_type=InterfaceAttachType.MACVLAN,
                 attach_name="eno2",
+                name="eth2",
             ),
         )
         self.assertEqual(
@@ -1028,6 +1031,7 @@ def test_get_discovered_machine(self):
                 boot=False,
                 attach_type=InterfaceAttachType.SRIOV,
                 attach_name="eno3",
+                name="eth3",
             ),
         )
         self.assertEqual(
@@ -1039,6 +1043,7 @@ def test_get_discovered_machine(self):
                 boot=False,
                 attach_type=InterfaceAttachType.SRIOV,
                 attach_name="eno3",
+                name="eth4",
             ),
         )
         self.assertEqual(
@@ -1050,6 +1055,7 @@ def test_get_discovered_machine(self):
                 boot=False,
                 attach_type=InterfaceAttachType.SRIOV,
                 attach_name="eno3",
+                name="eth5",
             ),
         )
         self.assertEqual([], discovered_machine.tags)