You may notice when using OpenStack, if you change the hostname, that change is not persistent over a reboot. This is because cloud-init updates the hostname on start-up.

Method 1

One method would be to simply prevent cloud-init from updating the hostname and manually changing it yourself.

[root@collector ~]# hostname -f
collector.novalocal

To make your hostname change survive a reboot, edit /etc/cloud/cloud.cfg:

[root@collector ~]# vim /etc/cloud/cloud.cfg

Comment out the below line:

cloud_init_modules:
...
# - update_hostname
...

Now if you change the hostname and reboot:

[root@collector ~]# hostnamectl set-hostname collector.pikedom.com
[root@collector ~]# reboot

Your hostname should remain in-place:

[root@collector ~]# hostname -f
collector.pikedom.copm

Method 2

A second method would be to configure cloud-init to set the hostname for you.

[root@collector ~]# vim /etc/cloud/cloud.cfg.d/99_hostname.cfg

Enter the following content:

#cloud-config
hostname: collector
fqdn: collector.pikedom.com

Reboot and check.