What I am trying to achieve is creating a Horizontal Pod Autoscaler able to scale worker pods according to a custom metric produced by a controller pod.

I already have Prometheus scraping, Prometheus Adapater, Custom Metric Server fully operational and scaling the worker deployment with a custom metric my_controller_metric produced by the worker pods already works.

Now my workerpods don't produce this metric anymore, but the controller does. It seems that the API autoscaling/v1 does not support this feature. I am able to specify the HPA with the autoscaling/v2beta1 API if necessary though.

Here is my spec for this HPA:

apiVersion: autoscaling/v2beta1
kind: HorizontalPodAutoscaler
metadata:
  name: my-worker-hpa
  namespace: work
spec:
  maxReplicas: 10
  minReplicas: 1
  scaleTargetRef:
    apiVersion: extensions/v1beta1
    kind: Deployment
    name: my-worker-deployment
  metrics:
  - type: Object
    object:
      target:
        kind: Deployment
        name: my-controller-deployment
      metricName: my_controller_metric
      targetValue: 1

When the configuration is applied with kubectl apply -f my-worker-hpa.yml I get the message:

horizontalpodautoscaler "my-worker-hpa" configured

Though this message seems to be OK, the HPA does not work. Is this spec malformed?

As I said, the metric is available in the Custom Metric Server with a kubectl get --raw "/apis/custom.metrics.k8s.io/v1beta1" | jq . | grep my_controller_metric.

This is the error message from the HPA:

Type           Status  Reason                 Message
----           ------  ------                 -------
AbleToScale    True    SucceededGetScale      the HPA controller was able to get the target's current scale
ScalingActive  False   FailedGetObjectMetric  the HPA was unable to compute the replica count: unable to get metric my_controller_metric: Deployment on work my-controller-deployment/unable to fetch metrics from custom metrics API: the server could not find the metric my_controller_metric for deployments

Thanks!