As you will see in this scenario, an application is being deployed on public Azure and on one or more Azure Stack environments. In combination with using DNS services and Azure Traffic manager, your environment automatically decides the proper cloud to answer an application request. If one is unavailable, it even automatically fails over to another one.
For more information, please refer to: https://docs.microsoft.com/en-us/azure/azure-stack/user/azure-stack-solution-geo-distributed.