Heat architecture

Heat is a service to orchestrate multiple composite cloud applications using the AWS CloudFormation template format, through both an OpenStack-native REST API and a CloudFormation-compatible Query API.

Detailed description

What is the purpose of the project and vision for it?

Heat provides an AWS CloudFormation implementation for OpenStack that orchestrates an AWS CloudFormation template describing a cloud application by executing appropriate OpenStack API calls to generate running cloud applications.

Describe the relevance of the project to other OpenStack projects and the OpenStack mission to provide a ubiquitous cloud computing platform:

The software integrates other core components of OpenStack into a one-file template system. The templates allow creation of most OpenStack resource types (such as instances, floating IPs, volumes, security groups and users), as well as some more advanced functionality such as instance high availability, instance autoscaling, and nested stacks. By providing very tight integration with other OpenStack core projects, all OpenStack core projects could receive a larger user base.

Currently no other CloudFormation implementation exists for OpenStack. The developers believe cloud developers have a strong desire to move workloads from AWS to OpenStack deployments. Given the missing gap of a well-implemented and integrated CloudFormation API in OpenStack, we provide a high quality implementation of this gap improving the ubiquity of OpenStack.

Heat services

The developers are focused on creating an OpenStack style project using OpenStack design tenets, implemented in Python. We have started with full integration with keystone. We have a number of components.

As the developers have only started development in March 2012, the architecture is evolving rapidly.


The heat tool is a CLI which communicates with the heat-api to execute AWS CloudFormation APIs. End developers could also use the heat REST API directly.


The heat-api component provides an OpenStack-native REST API that processes API requests by sending them to the heat-engine over RPC.


The heat-api-cfn component provides an AWS Query API that is compatible with AWS CloudFormation and processes API requests by sending them to the heat-engine over RPC.


The heat-engine’s main responsibility is to orchestrate the launching of templates and provide events back to the API consumer.

The templates integrate well with Puppet and Chef.