user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/attributes/?recursive=true&wait_for_change=true" -H "The metadata: Google"
user@myinst:~$ curl "http://metadata.google.internal/computeMetadata/v1/instance/attributes/?recursive=true&wait_for_change=true" -H "Metadata-Flavor: Google"