It has been requested that the user deploying the stack receive a callback notification during the lifecycle of a stack in order to insert custom steps/validation/whatever into the existing orchestration. This session is to discuss and finalize the design of such a feature and to get commitment for delivery in Juno.
Basically, the user would add template elements to define at both a stack and resource level, callback urls that Heat would call prior to the particular lifecycle event. The user would also be able to define response codes that Heat would use to determine if the stack could continue or should be marked as failed.
We could also allow the user to define their own payload using str_replace and other intrinsic functions. Authentication needs discussing.
We can determine the actual events but a rough guess: