The following are the main components for the Heat orchestration framework:
The Heat CLI
heat-api
heat-api-cfn
heat-engine
Heat Orchestration Template (HOT)
The Heat CLI is the command-line tool for Heat. It interacts with heat-api to run AWS CloudFormation commands; or otherwise, it can directly run REST API commands for Heat.
The heat-api component offers a REST API, which is OpenStack native. To process the user requests, this API forwards those requests to the Heat engine using the RPC.
The heat-api-cfn module offers another API that is compatible with AWS CloudFormation. It also processes queries after forwarding them to heat-engine over RPC.