Asking the question here, since there is no sufficient documentation available.

I have the HorizontalPodAutoscaler configuration like this below, I want to auto scale instances based on custom metrics provided by gke(google container engine) stackdriver monitoring. I want to scale based on number of requests.

  metrics:
  - type: Object
    object:
      metricName: requests-per-second
      target:
        apiVersion: extensions/v1beta1
        kind: Ingress
        name: main-route
      targetValue: 25