Unable to access the GCP metadata server from a pod

Issue

• The Google metadata server is not accessible from within a pod:

  $ oc rsh $POD curl -s "http://metadata.google.internal/computeMetadata/v1/instance/zone" -H "Metadata-Flavor: Google"
  command terminated with exit code 7
  

• Running the same command from the node or a pod with hostNetwork: true works:

  $ oc debug node/${NODE} -- curl -s "http://metadata.google.internal/computeMetadata/v1/instance/zone" -H "Metadata-Flavor: Google"
  Starting pod/pbertera-03285776-s9fkd-worker-a-x77wx-debug ...
  To use host binaries, run `chroot /host`
  projects/123456789/zones/europe-west3-a
  Removing debug pod ...