I am currently referring to google documentation for autoscaling using pubsub metric from stackdriver: Autoscaling Deployments with External Metrics

But, I am getting some error in deploying google sample config present in above link/config link: Link to config image

Error: error validating data: ValidationError(HorizontalPodAutoscaler.spec.metrics[0]): unknown field "external" in io.k8s.api.autoscaling.v2beta1.MetricSpec; if you choose to ignore these errors, turn validation off with --validate=false

Looked around the web but was unable to find any reference to this error. I am not sure what is wrong.