HPA could not get CPU metric during GKE node auto-scaling

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1

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Cluster information:

Kubernetes version: 1.12.8-gke.10
Cloud being used: GKE
Installation method: gcloud
Host OS: (machine type) n1-standard-1
CNI and version: default
CRI and version: default

During node scaling, HPA couldn’t get CPU metric. At the same time, kubectl top pod and kubectl top node output is:
Error from server (ServiceUnavailable): the server is currently unable to handle the request (get pods.metrics.k8s.io)
Error from server (ServiceUnavailable): the server is currently unable to handle the request (get nodes.metrics.k8s.io)

For more details, I’ll show you the flow of my problem occurs:

  1. Suddenly many requests arrive at the GKE server. (Using testing tool)
  2. HPA detects current CPU usage above target CPU usage(50%), thus try pod scale up
    incrementally.
  3. Insufficient CPU warning occurs when creating pods, thus GKE try node scalie up
    incrementally.
  4. Soon the HPA fails to get the metric, and kubectl top node or kubectl top pod
    doesn’t get a response.
    - At this time one or more OutOfcpu pods are found, and several pods are in
    ContainerCreating (from Pending state).
  5. After node scale-up is complete and some time has elapsed (about a few minutes),
    HPA starts to fetch the CPU metric successfully and try to scale up/down based on
    metric.
  6. Same situation happens when node scale down.

This causes pod scaling to stop and raises some failures on responding to client’s requests. Is this normal?

I think HPA should get CPU metric(or other metrics) on running pods even during node scaling, to keep track of the optimal pod size at the moment. So when node scaling done, HPA create the necessary pods at once (rather than incrementally).

Can I make my cluster work like this?

2

hey mate, I also have the same issue as of today and 2 things I have realised: 1- the metrics-server logs shows that it can’t scrape nodes, but the nodes doesn’t exist in k8s; 2) the API works fine, if I run kubectl top pods or kubectl top nodes it always shows both CPU and memory.

don’t know why metrics-server is behaving like this.