Heat CloudFormation (CFN) orchestration in OpenStack provides the ability to use AWS-style:
- APIs
- templates
- expressions within regular HOT templates
This means that operators coming from an AWS cloud environment to OpenStack can use their existing AWS APIs and templates to spin up tenant VMs, networks, etc., making the transition more seamless. For more information on Heat and Heat CFN, see https://wiki.openstack.org/wiki/Heat.
A very useful mechanism within AWS, and supported by Heat CFN is an AWS::CloudFormation::WaitCondition, which can be inserted in between two virtual resource instantiations, and causes the orchestration layer to wait until one resource is up and running before bringing up the next resource. This allows cloud orchestration to happen in a stable, predictable way. Further explanation and an example HOT template using an AWS::CloudFormation::WaitCondition can be found here: https://blog.zhaw.ch/icclab/manage-instance-startup-order-in-openstack-heat-templates/.
Interestingly, the OpenStack community is moving away from AWS APIs, and therefore from CFN. There are several reasons for this:
- The AWS APIs have not been properly maintained within OpenStack
- Heat CFN has a dependency on the Nova EC2 APIs, which have been deprecated
- HOT templates now have native support for WaitCondition
See http://cloudscaling.com/blog/openstack/the-future-of-openstacks-ec2-apis/ for more information.
Going forward, a standalone EC2 API is being maintained in StackForge, so it will still be possible to use CFN, however it will not be part of standard deployment.
