Supporting Multiple Persistence Models for PaaS Applications using MDE - Issues on Cloud Portability

In cloud computing, lock-in refers to the difficulty of porting an application from one platform to another. An example of such difficulty can be witnessed when porting an application from Platform-as-a-Service Google App Engine to Microsoft Azure. Differences in their implementations are substantial, yielding non-portable applications. Standardization could address this problem, but existing initiatives are still to be accepted. This paper addresses lock-in by proposing a model-driven engineering design approach that decouples platform specific code from the application logic. The resulting platform-independent models, as well as corresponding model transformations, can be reused to generate distinct platform-specific implementations, hence reducing the programming effort spent coding repetitive tasks. Such transformations can be made available for reuse on a repository for cloud providers. We have implemented transformations to handle persistence for Google App Engine and Azure, and discuss how model-driven engineering can reconcile the differences between features of the persistence models of GAE and Azure.