[Azure] Published hostname (ddns) gets reset on reboot after `hostnamectl set-hostname`

This bug was originally filed in Launchpad as [LP: #1755260](https://bugs.launchpad.net/cloud-init/+bug/1755260)

Launchpad details

affected_projects = []

assignee = None

assignee_name = None

date_closed = None

date_created = 2018-03-12T18:35:26.628172+00:00

date_fix_committed = None

date_fix_released = None

id = 1755260

importance = low

is_complete = False

lp_url = https://bugs.launchpad.net/cloud-init/+bug/1755260

milestone = None

owner = paul-meyer

owner_name = Paul Meyer

private = False

status = triaged

submitter = paul-meyer

submitter_name = Paul Meyer

tags = []

duplicates = []

_Launchpad user **Paul Meyer(paul-meyer)** wrote on 2018-03-12T18:35:26.628172+00:00_

Verified on Azure, using Trusty (Canonical:UbuntuServer:14.04.5-LTS:14.04.201803080) (cloud-init 0.7.5-0ubuntu1.22)

1. create a Trusty VM:
az vm create -g paulmey-test -n ubuntu14 --image Canonical:UbuntuServer:14.04.5-LTS:latest
2. On the VM, edit /etc/waagent.conf to set Provisioning.MonitorHostName=y and restart the agent.
This sets waagent to ifdown/ifup when it detects a hostname change such that the new hostname is
sent on the DHCP request, which in Azure populates the instance DNS.
3. verify 'nslookup ubuntu14' shows a DNS record for the initial hostname (ubuntu14)
4. run 'hostnamectl set-hostname seeifitsticks' to change the hostname
5. Wait a minute for the update to propagate, verify that 'nslookup seeifitsticks' now shows a DNS
record for the new hostname. Verify that /etc/hostname is updated. Verify that 'nslookup ubuntu14'
no longer returns a valid DNS record.
6. reboot the vm
7. Once back up, notice that the hostname is seeifitsticks. However, 'nslookup seeifitsticks' returns
NXDOMAIN, which 'nslookup ubuntu14' shows a DNS record.

From the cloud-init log, it looks like cloud-init sets the hostname to whatever is in the ovf-env.xml during interface bounce. On Xenial, the data source is loaded from cache, which is why this code does not even run.