DLPX-67281 Network configuration not migrated because of multiple netplan files

The root-cause of this issue is that the service that generates the
default netplan file for cloud-init (named cloud-init-local) can run
at the same time as delphix-migration which writes our own custom
netplan file on-disk (and potentially deletes the default one if the
timing is right). Unfortunately, timing is not always right and due
to the above raace between the two services we end up with two
netplan files that can have conflicting info.

This change ensures that the migration service runs after cloud-init-local
so the default netplan file is always generated before ouyr custom one
takes its place.

Note again that this is a migration-only issue that can happen on
first boot. We disable the cloud-init-local service from regenerating
its netplan file for subsequent boots.

Author: sdimitro

files/common/lib/systemd/system/delphix-migration.service

@@ -37,11 +37,22 @@
 # local-fs.target, it is better to be more explicit in case we decided to
 # remove the latter.
 #
+# The OS network migration code, even though it doesn't list the
+# netplan file generated by cloud-init as a hard dependency, it can
+# experience a race as the one pointed in DLPX-67281, where the
+# cloud-init-local service runs around the same time and generates
+# the default netplan file while we write our custom one on-disk
+# through the netconf-migrator. This is bad because we end up with two
+# netplan files that can have conflicting information for networkd.
+# To avoid this scenario, we make sure that this service runs AFTER
+# cloud-init-local.
+#
 [Unit]
 Description=Delphix OS Migration Service
 PartOf=delphix.target
 DefaultDependencies=no
 After=systemd-udev-settle.service
+After=cloud-init-local.service
 After=var-delphix.mount
 After=local-fs.target
 Before=network-pre.target