What you need for this book
To follow the examples in this book, you'll need an installation of OpenStack. This can be as big as multiple hardware machines or as little as a single virtual machine. For the goals of this book, it does not matter.
As for the operating system on the host, I suggest using CentOS/RHEL 6 or 7, because this is the configuration that is directly touched by the examples, but you can easily adapt the examples to any other Linux distribution.