Fix exception when no activator found (SC-540)

cloudinit/distros/__init__.py

@@ -228,7 +228,12 @@ def apply_network_config(self, netconfig, bring_up=False) -> bool:
         # Now try to bring them up
         if bring_up:
             LOG.debug('Bringing up newly configured network interfaces')
-            network_activator = activators.select_activator()
+            try:
+                network_activator = activators.select_activator()
+            except activators.NoActivatorException:
+                LOG.warning("No network activator found, not bringing up "
+                            "network interfaces")
+                return True
             network_activator.bring_up_all_interfaces(network_state)
         else:
             LOG.debug("Not bringing up newly configured network interfaces")

cloudinit/net/activators.py

@@ -16,6 +16,10 @@
 LOG = logging.getLogger(__name__)
 
 
+class NoActivatorException(Exception):
+    pass
+
+
 def _alter_interface(cmd, device_name) -> bool:
     LOG.debug("Attempting command %s for device %s", cmd, device_name)
     try:
@@ -271,7 +275,7 @@ def select_activator(priority=None, target=None) -> Type[NetworkActivator]:
         tmsg = ""
         if target and target != "/":
             tmsg = " in target=%s" % target
-        raise RuntimeError(
+        raise NoActivatorException(
             "No available network activators found%s. Searched "
             "through list: %s" % (tmsg, priority))
     selected = found[0]

tests/unittests/test_net_activators.py

@@ -12,7 +12,8 @@
     IfUpDownActivator,
     NetplanActivator,
     NetworkManagerActivator,
-    NetworkdActivator
+    NetworkdActivator,
+    NoActivatorException,
 )
 from cloudinit.net.network_state import parse_net_config_data
 from cloudinit.safeyaml import load
@@ -99,7 +100,7 @@ def test_none_available(self, unavailable_mocks):
         resp = search_activator()
         assert resp == []
 
-        with pytest.raises(RuntimeError):
+        with pytest.raises(NoActivatorException):
             select_activator()