This scenario describes an environment where the customer is running its application (for example, a web application) on Azure Stack on-premise and, based on an automatic or manually triggered process (for example, excessive load on the solution), the system auto scales to public Azure through traffic manager to ensure flexibility and scalability.
For more information, please refer to: https://docs.microsoft.com/en-us/azure/azure-stack/user/azure-stack-solution-cloud-burst.