In Chapter 9, Telemetry, Ceilometer alarms were introduced. These were monitoring objects that were able to trigger external actions based on a certain criterion being met for a predetermined set of iterations. Heat's autoscaling is the primary use case for this functionality. Using Heat's autoscaling, it is possible to monitor a set of instances and add or subtract instances to meet load demands. In the same GitHub repository that the previous examples were taken from, there is an autoscaling example. For the autoscaling example to work, you will need to grab two templates:

These templates are written to launch a single database instance and to add and remove web server instances respective to the load put on the WordPress stack running on the web servers.