Comment 25 for bug 1938299

To clarify the actual root cause here and reflect it back to this original bug.

   google-guest-agent defines a `PartOf=` relationship with systemd-networkd.service[1]. This relationship means that if systemd-networkd.service is either stopped, google-guest-agent.service gets stopped. When systemd-networkd.service is restarted, so is google-guest-agent.

But if systemd-networkd.service is subsequently started after a previous stop call, google-guest-agent is left in stopped state. The call `netplan apply` (emitted by cloud-init after writing network config) in fact calls systemctl stop systemd-networkd.service and follows it with a 'start' instead of directly invoking systemctl restart systemd-networkd.service[2]. This leaves google-guest in stopped state indefinitely.

I'm not entirely sure netplan can fix this issue due to some other cleanup they are doing between networkd stop and start, but I have reflected this bug to netplan.io folks and we'll see what the consensus is about whether this can be resolved with instrumenting a "systemctl restart" instead of separate "systemctl stop" and "systemctl start" calls.

References:
[1] https://github.com/GoogleCloudPlatform/guest-agent/blob/main/google-guest-agent.service#L13
[2] https://git.launchpad.net/ubuntu/+source/netplan.io/tree/netplan/cli/commands/apply.py?h=applied/ubuntu/devel#n169