Nested: Detect MTU mismatch

Apparently it is possible to override Neutron's MTU setting through DHCP
agent. This may lead to a situation when node (VM) network will have a
different MTU than pod network. In such case setting pod network's MTU
on a Pod's veth pair will fail due to MTU mismatch.

This commit makes sure we detect such situation soon and produce a log
message with a hint about the root cause.

Change-Id: Ib694950c77ac7c3fd480f579b627dc79bfceac85
Closes-Bug: 1863212

kuryr_kubernetes/cni/binding/nested.py

@@ -21,6 +21,7 @@ import pyroute2
 
 from kuryr_kubernetes.cni.binding import base as b_base
 from kuryr_kubernetes import config
+from kuryr_kubernetes import exceptions
 from kuryr_kubernetes.handlers import health
 from kuryr_kubernetes import utils
 
@@ -68,6 +69,16 @@ class NestedDriver(health.HealthHandler, b_base.BaseBindingDriver):
                 # TODO(vikasc): evaluate whether we should have stevedore
                 #               driver for getting the link device.
                 vm_iface_name = config.CONF.binding.link_iface
+                mtu = h_ipdb.interfaces[vm_iface_name].mtu
+                if mtu != vif.network.mtu:
+                    # NOTE(dulek): This might happen if Neutron and DHCP agent
+                    # have different MTU settings. See
+                    # https://bugs.launchpad.net/kuryr-kubernetes/+bug/1863212
+                    raise exceptions.CNIBindingFailure(
+                        f'MTU of interface {vm_iface_name} ({mtu}) does not '
+                        f'match MTU of pod network {vif.network.id} '
+                        f'({vif.network.mtu}). Please make sure pod network '
+                        f'has the same MTU as node (VM) network.')
 
                 args = self._get_iface_create_args(vif)
                 with h_ipdb.create(ifname=temp_name,

kuryr_kubernetes/exceptions.py

@@ -76,3 +76,9 @@ class MultiPodDriverPoolConfigurationNotSupported(Exception):
     2. One of the pod drivers is not supported
     3. One of the pod drivers is not supported by its selected pool driver
     """
+
+
+class CNIBindingFailure(Exception):
+    """Exception indicates a binding/unbinding VIF failure in CNI"""
+    def __init__(self, message):
+        super(CNIBindingFailure, self).__init__(message)

kuryr_kubernetes/tests/unit/cni/test_binding.py

@@ -21,6 +21,7 @@ from oslo_config import cfg
 from kuryr_kubernetes.cni.binding import base
 from kuryr_kubernetes.cni.binding import sriov
 from kuryr_kubernetes import constants as k_const
+from kuryr_kubernetes import exceptions
 from kuryr_kubernetes import objects
 from kuryr_kubernetes.tests import base as test_base
 from kuryr_kubernetes.tests import fake
@@ -60,6 +61,7 @@ class TestDriverMixin(test_base.TestCase):
                 'bridge': mock.Mock(
                     __enter__=mock.Mock(return_value=self.m_bridge_iface),
                     __exit__=mock.Mock(return_value=None),
+                    mtu=1,
                 ),
                 'c_interface': mock.Mock(
                     __enter__=mock.Mock(return_value=self.m_c_iface),
@@ -187,6 +189,10 @@ class TestNestedVlanDriver(TestDriverMixin, test_base.TestCase):
         self.assertEqual(str(self.vif.address), self.m_h_iface.address)
         self.m_h_iface.up.assert_called_once_with()
 
+    def test_connect_mtu_mismatch(self):
+        self.vif.network.mtu = 2
+        self.assertRaises(exceptions.CNIBindingFailure, self._test_connect)
+
     def test_disconnect(self):
         self._test_disconnect()
 
@@ -209,6 +215,10 @@ class TestNestedMacvlanDriver(TestDriverMixin, test_base.TestCase):
         self.assertEqual(str(self.vif.address), self.m_h_iface.address)
         self.m_h_iface.up.assert_called_once_with()
 
+    def test_connect_mtu_mismatch(self):
+        self.vif.network.mtu = 2
+        self.assertRaises(exceptions.CNIBindingFailure, self._test_connect)
+
     def test_disconnect(self):
         self._test_disconnect()