Merge ~oddbloke/cloud-init/+git/cloud-init:bugfix/release_blocker into cloud-init:master

[Dan Watkins]

DataSourceEc2: update RELEASE_BLOCKER to be more accurate

Our previous understanding of the upgrade issue was incomplete; it turns
out the only change we need is the one now outlined.

[Server Team CI bot (server-team-bot)]

PASSED: Continuous integration, rev:e0a4f697b32fc8b7f3162fb93b12fbb3d798bad3
https://jenkins.ubuntu.com/server/job/cloud-init-ci/636/
Executed test runs:
    SUCCESS: Checkout
    SUCCESS: Unit & Style Tests
    SUCCESS: Ubuntu LTS: Build
    SUCCESS: Ubuntu LTS: Integration
    IN_PROGRESS: Declarative: Post Actions

Click here to trigger a rebuild:
https://jenkins.ubuntu.com/server/job/cloud-init-ci/636/rebuild

review: Approve (continuous-integration)

[Ryan Harper (raharper)]

Let's add a comment about why we don'tneed a post-inst at this time.

review: Needs Fixing

[Ryan Harper (raharper)]

review: Approve

diff --git a/cloudinit/sources/DataSourceEc2.py b/cloudinit/sources/DataSourceEc2.py
index 4f2f6cc..ac28f1d 100644
--- a/cloudinit/sources/DataSourceEc2.py
+++ b/cloudinit/sources/DataSourceEc2.py
@@ -334,8 +334,12 @@ class DataSourceEc2(sources.DataSource):
         if isinstance(net_md, dict):
             result = convert_ec2_metadata_network_config(
                 net_md, macs_to_nics=macs_to_nics, fallback_nic=iface)
-            # RELEASE_BLOCKER: Xenial debian/postinst needs to add
-            # EventType.BOOT on upgrade path for classic.
+
+            # RELEASE_BLOCKER: xenial should drop the below if statement,
+            # because the issue being addressed doesn't exist pre-netplan.
+            # (This datasource doesn't implement check_instance_id() so the
+            # datasource object is recreated every boot; this means we don't
+            # need to modify update_events on cloud-init upgrade.)
 
             # Non-VPC (aka Classic) Ec2 instances need to rewrite the
             # network config file every boot due to MAC address change.