If the Kubernetes Metric Server does not reach the READY 1/1 state, run the following commands:

kubectl describe pod <metrics-server-pod> -n kube-system

kubectl logs <metrics-server-pod> -n kube-system

If you see errors such as:

Readiness probe failed: HTTP probe failed with statuscode: 500

and:

E0907 13:07:50.937308       1 scraper.go:140] "Failed to scrape node" err="Get \"https://X.X.X.X:10250/metrics/resource\": x509: cannot validate certificate for 100.105.18.113 because it doesn't contain any IP SANs" node="worker-node1"

then you may need to install a valid cluster certificate for your Kubernetes cluster.

For testing purposes, you can resolve this issue by:

1. Delete the Kubernetes Metrics Server by running the following command:

   kubectl delete -f $WORKDIR/kubernetes/hpa/components.yaml

2. Edit the $WORKDIR/hpa/components.yaml and locate the args: section. Add kubelet-insecure-tls to the arguments. For example:

   spec:
     containers:
     - args:
       - --cert-dir=/tmp
       - --secure-port=4443
       - --kubelet-preferred-address-types=InternalIP,ExternalIP,Hostname
       - --kubelet-use-node-status-port
       - --kubelet-insecure-tls
       - --metric-resolution=15s
       image: registry.k8s.io/metrics-server/metrics-server:v0.6.4
    ...

3. Deploy the Kubernetes Metrics Server using the command:

   kubectl apply -f components.yaml

4. Run the following and make sure the READY status shows 1/1:

   kubectl get pods -n kube-system | grep metric

   The output should look similar to the following:

   metrics-server-d9694457-mf69d           1/1     Running   0             40s