If you are running virtual machines today, you're already using a cloud-based technology, although we do not call it cloud today. Basically, this is the idea of a private cloud. If you are running Azure Pack today, you are quite near Azure Stack from the processes point of view but not the technology part. There is a solution called connectors for Azure Pack that lets you have one portal UI for both cloud solutions. This means that the customer can manage everything out of the Azure Stack Portal, although services run in Azure Pack as a legacy solution.

Basically, there is no real migration path within Azure Stack. But the way to solve this is quite easy, because you could use every tool that you can use to migrate services to Azure.