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']

3 files changed, 104 insertions, 5 deletions

diff --git a/tests/integration_tests/modules/test_user_events.py b/tests/integration_tests/modules/test_user_events.py
new file mode 100644
index 00000000..a45cad72
--- /dev/null
+++ b/tests/integration_tests/modules/test_user_events.py
@@ -0,0 +1,95 @@
+"""Test user-overridable events.
+
+This is currently limited to applying network config on BOOT events.
+"""
+
+import pytest
+import re
+import yaml
+
+from tests.integration_tests.instances import IntegrationInstance
+
+
+def _add_dummy_bridge_to_netplan(client: IntegrationInstance):
+    # Update netplan configuration to ensure it doesn't change on reboot
+    netplan = yaml.safe_load(
+        client.execute('cat /etc/netplan/50-cloud-init.yaml')
+    )
+    # Just a dummy bridge to do nothing
+    try:
+        netplan['network']['bridges']['dummy0'] = {'dhcp4': False}
+    except KeyError:
+        netplan['network']['bridges'] = {'dummy0': {'dhcp4': False}}
+
+    dumped_netplan = yaml.dump(netplan)
+    client.write_to_file('/etc/netplan/50-cloud-init.yaml', dumped_netplan)
+
+
+@pytest.mark.lxd_container
+@pytest.mark.lxd_vm
+@pytest.mark.ec2
+@pytest.mark.gce
+@pytest.mark.oci
+@pytest.mark.openstack
+@pytest.mark.not_xenial
+def test_boot_event_disabled_by_default(client: IntegrationInstance):
+    log = client.read_from_file('/var/log/cloud-init.log')
+    assert 'Applying network configuration' in log
+    assert 'dummy0' not in client.execute('ls /sys/class/net')
+
+    _add_dummy_bridge_to_netplan(client)
+    client.execute('rm /var/log/cloud-init.log')
+
+    client.restart()
+    log2 = client.read_from_file('/var/log/cloud-init.log')
+
+    # We attempt to apply network config twice on every boot.
+    # Ensure neither time works.
+    assert 2 == len(
+        re.findall(r"Event Denied: scopes=\['network'\] EventType=boot[^-]",
+                   log2)
+    )
+    assert 2 == log2.count(
+        "Event Denied: scopes=['network'] EventType=boot-legacy"
+    )
+    assert 2 == log2.count(
+        "No network config applied. Neither a new instance"
+        " nor datasource network update allowed"
+    )
+
+    assert 'dummy0' in client.execute('ls /sys/class/net')
+
+
+def _test_network_config_applied_on_reboot(client: IntegrationInstance):
+    log = client.read_from_file('/var/log/cloud-init.log')
+    assert 'Applying network configuration' in log
+    assert 'dummy0' not in client.execute('ls /sys/class/net')
+
+    _add_dummy_bridge_to_netplan(client)
+    client.execute('rm /var/log/cloud-init.log')
+    client.restart()
+    log = client.read_from_file('/var/log/cloud-init.log')
+
+    assert 'Event Allowed: scope=network EventType=boot' in log
+    assert 'Applying network configuration' in log
+    assert 'dummy0' not in client.execute('ls /sys/class/net')
+
+
+@pytest.mark.azure
+@pytest.mark.not_xenial
+def test_boot_event_enabled_by_default(client: IntegrationInstance):
+    _test_network_config_applied_on_reboot(client)
+
+
+USER_DATA = """\
+#cloud-config
+updates:
+  network:
+    when: [boot]
+"""
+
+
+@pytest.mark.not_xenial
+@pytest.mark.user_data(USER_DATA)
+def test_boot_event_enabled(client: IntegrationInstance):
+    _test_network_config_applied_on_reboot(client)
diff --git a/tests/unittests/test_datasource/test_azure.py b/tests/unittests/test_datasource/test_azure.py
index 742d1faa..54e06119 100644
--- a/tests/unittests/test_datasource/test_azure.py
+++ b/tests/unittests/test_datasource/test_azure.py
@@ -3163,8 +3163,8 @@ class TestRemoveUbuntuNetworkConfigScripts(CiTestCase):
 
         expected_logs = [
             'INFO: Removing Ubuntu extended network scripts because cloud-init'
-            ' updates Azure network configuration on the following event:'
-            ' System boot.',
+            ' updates Azure network configuration on the following events:'
+            " ['boot', 'boot-legacy']",
             'Recursively deleting %s' % subdir,
             'Attempting to remove %s' % file1]
         for log in expected_logs:
diff --git a/tests/unittests/test_datasource/test_smartos.py b/tests/unittests/test_datasource/test_smartos.py
index 5847a384..9c499672 100644
--- a/tests/unittests/test_datasource/test_smartos.py
+++ b/tests/unittests/test_datasource/test_smartos.py
@@ -29,7 +29,7 @@ from cloudinit.sources.DataSourceSmartOS import (
     convert_smartos_network_data as convert_net,
     SMARTOS_ENV_KVM, SERIAL_DEVICE, get_smartos_environ,
     identify_file)
-from cloudinit.event import EventType
+from cloudinit.event import EventScope, EventType
 
 from cloudinit import helpers as c_helpers
 from cloudinit.util import (b64e, write_file)
@@ -653,8 +653,12 @@ class TestSmartOSDataSource(FilesystemMockingTestCase):
     def test_reconfig_network_on_boot(self):
         # Test to ensure that network is configured from metadata on each boot
         dsrc = self._get_ds(mockdata=MOCK_RETURNS)
-        self.assertSetEqual(set([EventType.BOOT_NEW_INSTANCE, EventType.BOOT]),
-                            dsrc.update_events['network'])
+        self.assertSetEqual(
+            {EventType.BOOT_NEW_INSTANCE,
+             EventType.BOOT,
+             EventType.BOOT_LEGACY},
+            dsrc.default_update_events[EventScope.NETWORK]
+        )
 
 
 class TestIdentifyFile(CiTestCase):