We have many tools paid and free to help us migrate workloads to cloud. There are a very few for Platform-as-a-service apps. It is believed that most of the time PaaS requires application re-write. However, a well-designed futuristic modern web application is ready for App Services most of the time.
Microsoft provides state of the art utility to perform the same for both Windows and Linux to help you web applications to cloud, mainly Web Apps. For more visit https://www.movemetothecloud.net/