https://cloud.google.com/ml/docs/concepts/training-overview mentions the following:
If your trainer application has any dependencies that are not already on the default virtual machines that Cloud ML uses, you must package them and upload them to a Google Cloud Storage location as well.
What is "already on the default virtual machines that Cloud ML uses"? I couldn't find this info anywhere.
Incidentally, are there any published specs of the machine types here? https://cloud.google.com/ml/reference/rest/v1beta1/projects.jobs#ScaleTier