Autoresizing Persistent Disks in Compute Engine

Yes, of course they're correct; however, invoking gcloud is comparatively much slower than just curl'ing against the metadata server (you know, no Python code to interpret in the latter case).

With regards to JSON, not sure what you mean, since getting e.g. instance zone from metadata server gives you a plain text string like "projects/<PROJECT_NUMBER>/zones/europe-west1-d". AFAIK, the only way to get JSON-like results is by making recursive requests, such as:

  $ curl -H 'Metadata-Flavor: Google' "http://metadata/computeMetadata/v1/instance/?recursive=true"

And even in that case, you can choose plain text format by appending "alt=text" as query string parameter:

  $ curl -H 'Metadata-Flavor: Google' "http://metadata/computeMetadata/v1/instance/?recursive=true&alt=text"

Before IAM, the issue I had with service accounts is that I forgot to give the account Edit permissions. It seems the new way is like how @i_have_to_speak mentioned to use service account for an instance, which can only be done during creation of the instance, if you don't want to distribute keys. Then the newest way, that's still in beta, is to use IAM roles to further restrict the access scopes of that instance service account.