Allow user control over update events (#834)

Control is currently limited to boot events, though this should
allow us to more easily incorporate HOTPLUG support. Disabling
'instance-first-boot' is not supported as we apply networking config
too early in boot to have processed userdata (along with the fact
that this would be a pretty big foot-gun).

The concept of update events on datasource has been split into
supported update events and default update events. Defaults will be
used if there is no user-defined update events, but user-defined
events won't be supplied if they aren't supported.
When applying the networking config, we now check to see if the event
is supported by the datasource as well as if it is enabled.

Configuration looks like:
updates:
  network:
    when: ['boot']

1 files changed, 18 insertions, 11 deletions

diff --git a/cloudinit/sources/tests/test_init.py b/cloudinit/sources/tests/test_init.py
index 1420a988..a2b052a6 100644
--- a/cloudinit/sources/tests/test_init.py
+++ b/cloudinit/sources/tests/test_init.py
@@ -5,7 +5,7 @@ import inspect
 import os
 import stat
 
-from cloudinit.event import EventType
+from cloudinit.event import EventScope, EventType
 from cloudinit.helpers import Paths
 from cloudinit import importer
 from cloudinit.sources import (
@@ -618,24 +618,29 @@ class TestDataSource(CiTestCase):
         self.assertEqual('himom', getattr(self.datasource, cached_attr_name))
         self.assertEqual('updated', self.datasource.myattr)
 
+    @mock.patch.dict(DataSource.default_update_events, {
+        EventScope.NETWORK: {EventType.BOOT_NEW_INSTANCE}})
+    @mock.patch.dict(DataSource.supported_update_events, {
+        EventScope.NETWORK: {EventType.BOOT_NEW_INSTANCE}})
     def test_update_metadata_only_acts_on_supported_update_events(self):
-        """update_metadata won't get_data on unsupported update events."""
-        self.datasource.update_events['network'].discard(EventType.BOOT)
+        """update_metadata_if_supported wont get_data on unsupported events."""
         self.assertEqual(
-            {'network': set([EventType.BOOT_NEW_INSTANCE])},
-            self.datasource.update_events)
+            {EventScope.NETWORK: set([EventType.BOOT_NEW_INSTANCE])},
+            self.datasource.default_update_events
+        )
 
         def fake_get_data():
             raise Exception('get_data should not be called')
 
         self.datasource.get_data = fake_get_data
         self.assertFalse(
-            self.datasource.update_metadata(
+            self.datasource.update_metadata_if_supported(
                 source_event_types=[EventType.BOOT]))
 
+    @mock.patch.dict(DataSource.supported_update_events, {
+        EventScope.NETWORK: {EventType.BOOT_NEW_INSTANCE}})
     def test_update_metadata_returns_true_on_supported_update_event(self):
-        """update_metadata returns get_data response on supported events."""
-
+        """update_metadata_if_supported returns get_data on supported events"""
         def fake_get_data():
             return True
 
@@ -643,14 +648,16 @@ class TestDataSource(CiTestCase):
         self.datasource._network_config = 'something'
         self.datasource._dirty_cache = True
         self.assertTrue(
-            self.datasource.update_metadata(
+            self.datasource.update_metadata_if_supported(
                 source_event_types=[
                     EventType.BOOT, EventType.BOOT_NEW_INSTANCE]))
         self.assertEqual(UNSET, self.datasource._network_config)
+
         self.assertIn(
             "DEBUG: Update datasource metadata and network config due to"
-            " events: New instance first boot",
-            self.logs.getvalue())
+            " events: boot-new-instance",
+            self.logs.getvalue()
+        )
 
 
 class TestRedactSensitiveData(CiTestCase):