Heat is an “orchestration service to launch multiple composite cloud applications using templates.”
The user of Heat defines virtual infrastructure ‘stacks’ as a template, a simple YAML file describing resources and their relations—servers, volumes, floating IPs, networks, security groups, users, etc. Using this template, Heat “orchestrates” the full lifecycle of a complete stack. Heat provisions the infrastructure, making all the calls to create the underlying parts and to wire them together. To make changes, the user modifies the template and updates the existing stack, and Heat makes the right changes. When the stack is decommissioned, Heat deletes all the allocated resources.