// specified, in-range, and not in use it will be used, otherwise the
  // operation will fail.  If not specified, a port will be allocated if this
  // Service requires one.  If this field is specified when creating a
  // Service which does not need it, creation will fail. This field will be
  // wiped when updating a Service to no longer need it (e.g. changing type
  // from NodePort to ClusterIP).