With Heat, we can create a wide variety of templates—from spinning up basic instances to creating complete environments for an application. In this section, we will show the basics of Heat by spinning up an instance, attaching it to an existing Neutron network, and assigning a floating IP to it. Heat templates, known as Heat Orchestration Templates (HOT) are Yet Another Markup Language (YAML) based files. The files describe the resources being used, the type and size of the instances, and the network an instance will be attached to, among other pieces of information required to run that environment.
In this section, we will show how to use a HOT file to spin up two web servers running Apache that are connected to a third instance running HA Proxy.