On CentOS 7 (systemd based), with cloud-init 0.7.5, cc_update_hostname will *always* overwrite the hostname, even if it shouldn't.
This is pretty easy to reproduce:
1) Add a 'hostname: metadata.example.com' to your user-data
2) Run 'hostnamectl set-hostname test.example.com'
3) Reboot the server
4) Check the hostname, it'll still be 'metadata.example.com'
5) Repeat 2-4, hostname will still be set
Looking at the code, this is because rhel.py doesn't populate the previous-hostname file correctly:
def _write_hostname(self, hostname, out_fn):
if self._dist_uses_systemd():
util.subp(['hostnamectl', 'set-hostname', str(hostname)])
else:
host_cfg = {
'HOSTNAME': hostname,
}
rhel_util.update_sysconfig_file(out_fn, host_cfg)
So, Distros::update_hostname calls _write_hostname to try and save the previous hostname to /var/lib/cloud/data/previous-hostname .. however, all this does is run the hostnamectl command, which doesn't actually update this file. This means that on the next cloud-init run, /var/lib/cloud/data/previous-hostname doesn't exist so the hostname gets blindly updated again.
The fix here seems pretty simple, we just need to update previous-hostname as well when running hostnamectl. I attached a patch that does this, though I don't know the best way to implement this.. my patch fails if cloud-init's data path is changed
I can confirm this bug. If you place the previous-hostname file manually it stops changing the hostname on every reboot. As a workaround i installed cloud-init-