Install custom Canonical Kubernetes on machines

By default, the version field in the machine specifications will determine which Canonical Kubernetes is downloaded from the stable rist level. While you can install different versions of the stable risk level by changing the version field, extra steps should be taken if you’re willing to install a specific risk level. This guide walks you through the process of installing custom Canonical Kubernetes on workload cluster machines.

Prerequisites

To follow this guide, you will need:

• A Kubernetes management cluster with Cluster API and providers installed and configured.

• A generated cluster spec manifest

Please refer to the getting-started guide for further details on the required setup.

In this guide we call the generated cluster spec manifrst cluster.yaml.

Overwrite the existing install.sh script

The installation of the Canonical Kubernetes snap is done via running the install.sh script in the cloud-init. While this file is automatically placed in every workload cluster machine which hard-coded content by Canonical Kubernetes providers, you can overwrite this file to make sure your desired content is available in the script.

As an example, let’s overwrite the install.sh for our control plane nodes. Inside the cluster.yaml, add the new file content:

apiVersion: controlplane.cluster.x-k8s.io/v1beta2
kind: CK8sControlPlane
...
spec:
  ...
  spec:
    files:
    - content: |
        #!/bin/bash -xe
        snap install k8s --classic --channel=latest/edge
      owner: root:root
      path: /capi/scripts/install.sh
      permissions: "0500"

Now the new control plane nodes that are created using this manifest will have the latest/edge Canonical Kubernetes snap installed on them!

Use preRunCommands

As mentioned above, the install.sh script is responsible for installing Canonical Kubernetes snap on machines. preRunCommands are executed before install.sh. You can also add an install command to the preRunCommands in order to install your desired Canonical Kubernetes version.

Note

Installing the Canonical Kubernetes snap via the preRunCommands, does not prevent the install.sh script from running. Instead, the installation process in the install.sh will fail with a message indicating that k8s is already installed. This is not considered a standard way and overwriting the install.sh script is recommended.

Edit the cluster.yaml to add the installation command:

apiVersion: controlplane.cluster.x-k8s.io/v1beta2
kind: CK8sControlPlane
...
spec:
  ...
  spec:
    preRunCommands:
    - snap install k8s --classic --channel=latest/edge