Over the past decade, cloud services emerged as one of the most promising technologies in IT. Since cloud computing allows improving the quality of software and, at the same time, aims at reducing costs of operating software and hardware, more and more software is delivered as a service in the cloud. However , moving existing software applications to the cloud and making them behave as software as a service is still a major challenge. In fact, in addition to technical aspects, business aspects also need to be considered. The ARTIST EU project (FP7) proposes a comprehensive model-based modernization approach, covering both business and technical aspects, to cloudify already existing software. In particular , ARTIST employs MDE techniques to automate the reverse engineering and forward engineering phases in a way that modernized software truly benefits from targeted cloud environments. In this paper we describe the overall ARTIST approach and present several lessons learned.