Rebooting an openstack instance causes the hostname to change

Issue

We have noticed that when we reboot instances - the instances' hostname changes from what it was when the instance was first created.

There are 2 distinct changes we have noticed.

The new hostname is the same as the original hostname except with '.localdomain' appended at the end.
The new hostname is changed to 'host-' with the private IP the instance gets from its neutron subnet appended at the end. e.g. 'host-192-168-0-20'

How can we prevent any and all hostname changes when rebooting instances?

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