Kubelets

Abstract

A kubelet in every node.

Kubelets#

The kubelet can be thought of as the most basic unit of a Kubernetes cluster since one is required on every node, including the control planes. It kind of ties the room together, so don’t let it get wet.

Preparing Worker nodes#

Hypothetically the only things that required to tie the worker nodes together should be the control plane and the kubelet running on them. There are some limitations or difficulties. The author’s understanding at the time of writing is that running Windows worker nodes in concert with *nix worker nodes is not a simple proposition. The reason for this is irrelevant since we’ll be running Linux, ArchLinux specifically, for all of our nodes.

That said, as long as your nodes are all running a version of Linux, you should be able to run a kubelet on them and join it to your control plane without too much fuss.

The editorial staff of whatever entity controls the creation and distribution of this work is much too lazy and solipsistic to go into a detailed explanation of the process here, so to cover all the bases, make sure to RTFM on the actual manual’s site.

Installation#

Since we’re all friends who know how to use ArchLinux, we’ll go ahead and install the kubelet on three of our computers using the command below.

  1. Install kubelet with yay on all of your worker nodes.

    yay -S kubelet

    1. For the contrarians, you may also install the kubelet from the AUR manually.

      1. Clone the related repository.

        git clone https://aur.archlinux.org/kubelet.git

      2. Update your working directory.

        cd kubelet

      3. Use makepkg to create and install the package.

        makepkg -si

    But enough showing off, back to the salt mines.

  2. Enable the kubelet with systemd

    sudo systemctl enable kubelet

Join the cluster#

This process is completed in three simple steps.

  1. Connect to the control plane.

    ssh the-control-plane

    1. Check the control plane node status.

      kubectl get nodes

  2. Use kubeadm to print your join command.

    sudo kubeadm token create --print-join-command

  3. Connect to your worker nodes individually, or using a configuration management tool like Ansible[1]

    ssh {worker-node-one,worker-node-two,worker-node-three}

  4. Run the join command obtained above for each node you need to join.

    run this on each node to be joined#
    kubeadm join 192.168.100.5:6443 --token abcdef.abcdefghijklmnop \
 --discovery-token-ca-cert-hash sha256:eba12bf8e45c71c0747df39212f0f7d7d6c4b88a9d82fd44a70d6b0b247415c2
    a successful join#
    [preflight] Running pre-flight checks
     [WARNING Swap]: swap is supported for cgroup v2 only. The kubelet must
       be properly configured to use swap. Please refer to
       https://kubernetes.io/docs/concepts/architecture/nodes/#swap-memory,
       or disable swap on the node
     [WARNING Service-Kubelet]: kubelet service is not enabled, please run
       'systemctl enable kubelet.service'
[preflight] Reading configuration from the "kubeadm-config" ConfigMap
   in namespace "kube-system"...
[preflight] Use 'kubeadm init phase upload-config --config your-config-file'
   to re-upload it.
[kubelet-start] Writing kubelet configuration to file
   "/var/lib/kubelet/config.yaml"
[kubelet-start] Writing kubelet environment file with flags to file
   "/var/lib/kubelet/kubeadm-flags.env"
[kubelet-start] Starting the kubelet
[kubelet-check] Waiting for a healthy kubelet at
   http://127.0.0.1:10248/healthz. This can take up to 4m0s
[kubelet-check] The kubelet is healthy after 3.502506434s
[kubelet-start] Waiting for the kubelet to perform the TLS Bootstrap

This node has joined the cluster:
* Certificate signing request was sent to apiserver and a response was
  received.
* The Kubelet was informed of the new secure connection details.

Run 'kubectl get nodes' on the control-plane to see this node join the
cluster.

If this completes without error, congratulations, you’re probably wondering why none of your nodes will show ready in your cluster. For that, we’ll need to install a Networking Add On.

This will be covered next week’s post, Flannel for networking.

Quick and Dirty control plane with kubeadm   Easy RSA
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