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Kubernetes Architecture - Kubelet in control plane?

Hello,
I just started the The Linux Foundation's LFS258 Kubernetes Fundamentals class and I am a little confused regarding the kubelets and the control plane.
Because in the official Kubernetes overview (https://kubernetes.io/docs/concepts/overview/components/) there are no kubelets in the control plane, but in the course architecture overview, there is a kubelet in the control plane.

I thought kubelets would only be necessary on worker nodes.

So, what is correct?
Is it possible to have kubelets in the control plane, because the control plane is also a node? Or is there another reason?

Thank you for your help!

Best Answer

  • chrispokorni
    chrispokorni Posts: 1,458
    Answer ✓

    Hi @foehlschlaeger,

    I agree that the documentation's ambiguous description of the kubelet node agent does not quite clarify its purpose.

    Both kubelet and kube-proxy node agents are found on every node of the cluster, that includes control-plane node(s) and worker nodes. One of kubelet's tasks is to coordinate with the container runtime the container lifecycle events: to start, stop, delete... Since the control-plane agents (api server, scheduler, controller-manager, etcd) are in fact containers, it is easy to see the need for a kubelet agent on a control-plane node as well.

    Regards,
    -Chris

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