App Engine Flexible is a PaaS (Platform-as-a-Service) with the mission that you bring the code and we do the rest for you. As an example, although we run the app as a Docker container, one doesn't need to understand Docker at all to get started. :-) It's a great place to get started without needing to understand how the infrastructure works. However, if you'd like to go beyond and provide your own Docker container, that works too. That is one of the exciting things we're making available with this new version.
In addition to App Engine Flexible, you can deploy Docker container to both Container Engine and regular GCE VMs in Google Cloud Platform. Each different offering will come with different set of features and different investment level on the user's side. A GCE VM will probably be the one with the ultimate flexibility on what one can do, but will typically require more time investment.
Regarding starting the container lazily and suspending it while inactive, that is not currently supported.
In addition to App Engine Flexible, you can deploy Docker container to both Container Engine and regular GCE VMs in Google Cloud Platform. Each different offering will come with different set of features and different investment level on the user's side. A GCE VM will probably be the one with the ultimate flexibility on what one can do, but will typically require more time investment.
Regarding starting the container lazily and suspending it while inactive, that is not currently supported.