For .NET version 3.1 and earlier, Google Cloud Tools for Visual Studio
automatically supplies an app.yaml file and a Dockerfile when you deploy to
App Engine. However, you can extend the .NET runtime to add additional
functionality by customizing the Docker image. For more information, see
Custom Runtimes.
Health checking
By default, all programs running in the flexible environment receive health check requests, and you don't need to write any additional code.