Using Heat ResourceGroup resources

This has come up a few times recently, so I wanted to share a howto showing how (and how not) to use the group resources in Heat, e.g OS::Heat::ResourceGroup and OS::Heat::AutoScalingGroup.

The key thing to remember when dealing with these resources is that they can multiply any number of resources (expressed as a heat stack), not just individual resources. This is a very cool feature when you get your head around it! :)

Lets go through a worked example, where we use ResourceGroup to create 5 identical servers, each with a cinder volume of the same size attached.