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, 62 insertions, 7 deletions

diff --git a/cloudinit/event.py b/cloudinit/event.py
index f7b311fb..76a0afc6 100644
--- a/cloudinit/event.py
+++ b/cloudinit/event.py
@@ -1,17 +1,72 @@
 # This file is part of cloud-init. See LICENSE file for license information.
-
 """Classes and functions related to event handling."""
 
+from enum import Enum
+from typing import Dict, Set
+
+from cloudinit import log as logging
+
+LOG = logging.getLogger(__name__)
+
 
-# Event types which can generate maintenance requests for cloud-init.
-class EventType(object):
-    BOOT = "System boot"
-    BOOT_NEW_INSTANCE = "New instance first boot"
+class EventScope(Enum):
+    # NETWORK is currently the only scope, but we want to leave room to
+    # grow other scopes (e.g., STORAGE) without having to make breaking
+    # changes to the user config
+    NETWORK = 'network'
 
-    # TODO: Cloud-init will grow support for the follow event types:
-    # UDEV
+    def __str__(self):  # pylint: disable=invalid-str-returned
+        return self.value
+
+
+class EventType(Enum):
+    """Event types which can generate maintenance requests for cloud-init."""
+    # Cloud-init should grow support for the follow event types:
+    # HOTPLUG
     # METADATA_CHANGE
     # USER_REQUEST
 
+    BOOT = "boot"
+    BOOT_NEW_INSTANCE = "boot-new-instance"
+    BOOT_LEGACY = "boot-legacy"
+
+    def __str__(self):  # pylint: disable=invalid-str-returned
+        return self.value
+
+
+def userdata_to_events(user_config: dict) -> Dict[EventScope, Set[EventType]]:
+    """Convert userdata into update config format defined on datasource.
+
+    Userdata is in the form of (e.g):
+    {'network': {'when': ['boot']}}
+
+    DataSource config is in the form of:
+    {EventScope.Network: {EventType.BOOT}}
+
+    Take the first and return the second
+    """
+    update_config = {}
+    for scope, scope_list in user_config.items():
+        try:
+            new_scope = EventScope(scope)
+        except ValueError as e:
+            LOG.warning(
+                "%s! Update data will be ignored for '%s' scope",
+                str(e),
+                scope,
+            )
+            continue
+        try:
+            new_values = [EventType(x) for x in scope_list['when']]
+        except ValueError as e:
+            LOG.warning(
+                "%s! Update data will be ignored for '%s' scope",
+                str(e),
+                scope,
+            )
+            new_values = []
+        update_config[new_scope] = set(new_values)
+
+    return update_config
 
 # vi: ts=4 expandtab