Ceilometer is a tool that collects usage and performance data, while Heat orchestrates complex deployments on top of OpenStack. Heat aims to autoscale its deployments, scaling up when they're running hot and scaling back when idle.
Ceilometer can access decisive data and trigger the appropriate actions in Heat. The result of these two OpenStack projects meeting is value creation in the form of an alarming API in Ceilometer and its consumption in Heat.
Slides presented at the Fall OpenStack Design Summit in Hong Kong