I have a custom metrics configured.

When I run:

kubectl get --raw "/apis/custom.metrics.k8s.io/v1beta1/namespaces/my-namespace/deployments.extensions/sample-app/queue_length" | jq

I got:

...
  "items": [
    {
      "describedObject": {
        "kind": "Deployment",
        "namespace": "my-namespace",
        "name": "sample-app",
        "apiVersion": "extensions/v1beta1"
      },
      "metricName": "queue_length",
      "timestamp": "2018-10-09T18:14:15Z",
      "value": "30"
    }
  ]
...

So I want to scale my deployment with this metric:

kind: HorizontalPodAutoscaler
apiVersion: autoscaling/v2beta1
metadata:
  name: sample-app
  namespace: my-namespace
spec:
  scaleTargetRef:
    apiVersion: extensions/v1beta1
    kind: Deployment
    name: sample-app
  minReplicas: 1
  maxReplicas: 10
  metrics:
  - type: Object
    object:
      metricName: queue_length
      target:
        apiVersion: extensions/v1beta1
        kind: Deployment
        name: sample-app
      targetValue: 20

But it doesn't seem to work, maybe I have to specify - type: Object somewhat different.

I tried to change kind to deployments, deployments.extension, deployments.extensions etc, but I keep getting error FailedGetScale

Upd.: I figured out that namespace for HPA object and target object should be the same, so I changed it. And now I'm getting

the HPA was unable to compute the replica count: unable to get metric queue_length: Deployment on default sample-app/unable to fetch metrics from custom metrics API: the server could not find the metric queue_length for deployments.extensions sample-app

Upd2.: Figured it out: hpa was in namespace default, while metric was exposed to my-namespace. So, should be careful with namespaces!