The Cloud Computing paradigm is used by many actors, whether companies or individuals in order to harness the power and agility of remote computing resources. Because they target developers and offer a smooth and easy way to deploy modern enterprise software without dealing with the underlying infrastructure, there is a steadily increasing interest for Platforms as a Service (PaaS). However, the lock-in makes the migration to another platform difficult. If the vendor decides to raise its prices or change its security policies, the customer may have to consider to move to the competition or suffer from these changes. Assistance and tooling to move to the competition at the PaaS layer still does not exist thus requiring tremendous re-engineering effort. In this regard, we propose an approach to the challenge of software migration between PaaS using Model-Driven Engineering coupled to Program Transformation.