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Create a Raspberry Pi 4 Cluster#

You can deploy the k0s distribution of Kubernetes to a cluster comprised of Raspberry Pi 4 Computers with Ubuntu 20.04 LTS as the operating system.

Prerequisites#

Install the following tools on your local system:

Note: If you use lower spec Raspberry Pi machines, it may be necessary to manually edit the example code and k0s configuration.

Install k0s#

Set up hardware and operating system#

Download and install the Ubuntu Server 20.04.1 LTS RASPI 4 Image.

Note: In addition to the documentation Ubuntu provides documentation on installing Ubuntu on Raspberry Pi Computers, the Raspberry Pi Foundation offers animaging tool that you can use to write the Ubuntu image to your noe SD cards.

Once cloud-init finishes bootstrapping the system, the default login credentials are set to user ubuntu with password ubuntu (which you will be prompted to change on first login).

Network configurations#

Note: For network configurtion purposes, this documentation assumes that all of your computers are connected on the same subnet.

Review the k0s required ports documentation to ensure that your network and firewall configurations allow necessary traffic for the cluster.

Review the Ubuntu Server Networking Configuration Documentation to ensure that all systems have a static IP address on the network, or that the network is providing a static DHCP lease for the nodes.

OpenSSH#

Ubuntu Server deploys and enables OpenSSH by default. Confirm, though, that for whichever user you will deploy the cluster with on the build system, their SSH Key is copied to each node's root user. Before you start, the configuration should be such that the current user can run:

ssh root@${HOST}

Where ${HOST} is any node and the login can succeed with no further prompts.

Set up Nodes#

Every node (whether control plane or not) requires additional configuration in preparation for k0s deployment.

cgroup Configuration#

  1. Ensure that the following packages are installed on each node:

    apt-get install cgroup-lite cgroup-tools cgroupfs-mount

  2. Enable the memory cgroup in the Kernel by adding it to the Kernel command line.

  3. Open the file /boot/firmware/cmdline.txt (responsible for managing the Kernel parameters), and confirm that the following parameters exist (and add them as necessary):

    cgroup_enable=cpuset cgroup_enable=memory cgroup_memory=1

  4. Be sure to reboot each node to ensure the memory cgroup is loaded.

Swap (Optional)#

While swap is technically optional, enable it to ease memory pressure.

  1. To create a swapfile:

    fallocate -l 2G /swapfile && \
chmod 0600 /swapfile && \
mkswap /swapfile && \
swapon -a

  2. Ensure that the usage of swap is not too agressive by setting the sudo sysctl vm.swappiness=10 (the default is generally higher) and configuring it to be persistent in /etc/sysctl.d/*.

  3. Ensure that your swap is mounted after reboots by confirming that the following line exists in your /etc/fstab configuration:

    /swapfile         none           swap sw       0 0

Kernel Modules#

Ensure the loading of the overlay, nf_conntrack and br_netfilter modules:

modprobe overlay
modprobe nf_conntrack
modprobe br_netfilter

In addition, add each of these modules to your /etc/modules-load.d/modules.conf file to ensure they persist following reboot.

Download k0s#

Download a k0s release. For example:

wget -O /tmp/k0s https://github.com/k0sproject/k0s/releases/download/v1.24.4+k0s.0/k0s-v1.24.4+k0s.0-arm64 # replace version number!
sudo install /tmp/k0s /usr/local/bin/k0s

-- or --

Use the k0s download script (as one command) to download the latest stable k0s and make it executable in /usr/bin/k0s.

curl -sSLf https://get.k0s.sh | sudo sh

At this point you can run k0s:

k0s version

v1.24.4+k0s.0

Deploy Kubernetes#

Each node can now serve as a control plane node or worker node.

Control Plane Node#

Use a non-ha control plane with a single node.

Systemd Service (controller)#

  1. Create a systemd service:

    sudo k0s install controller

  2. Start the service:

    sudo k0s start

  3. Run sudo k0s status or systemctl status k0scontroller to verify the service status.

Worker Tokens#

For each worker node that you expect to have, create a join token:

k0s token create --role worker

Save the join token for subsequent steps.

Worker#

You must deploy and start a worker service for each worker nodes for which you created join tokens.

Systemd Service (worker)#

  1. Create the join token file for the worker (where TOKEN_CONTENT is one of the join tokens created in the control plane setup):

    mkdir -p /var/lib/k0s/
echo TOKEN_CONTENT > /var/lib/k0s/join-token

  2. Deploy the systemd service for the worker:

    sudo k0s install worker --token-file /var/lib/k0s/join-token

  3. Start the service:

    sudo k0s start

  4. Run sudo k0s status or systemctl status k0sworker to verify the service status.

Connect To Your Cluster#

Generate a kubeconfig for the cluster and begin managing it with kubectl (where CONTROL_PLANE_NODE is the control plane node address):

ssh root@CONTROL_PLANE_NODE k0s kubeconfig create --groups "system:masters" k0s > config.yaml
export KUBECONFIG=$(pwd)/config.yaml
kubectl create clusterrolebinding k0s-admin-binding --clusterrole=admin --user=k0s

You can now access and use the cluster:

kubectl get nodes,deployments,pods -A

NAME         STATUS   ROLES    AGE     VERSION
node/k8s-4   Ready    <none>   5m9s    v1.24.4+k0s
node/k8s-5   Ready    <none>   5m      v1.24.4+k0s
node/k8s-6   Ready    <none>   4m45s   v1.24.4+k0s

NAMESPACE     NAME                                      READY   UP-TO-DATE   AVAILABLE   AGE
kube-system   deployment.apps/calico-kube-controllers   1/1     1            1           12m
kube-system   deployment.apps/coredns                   1/1     1            1           12m

NAMESPACE     NAME                                           READY   STATUS        RESTARTS   AGE
kube-system   pod/calico-kube-controllers-5f6546844f-rjdkz   1/1     Running       0          12m
kube-system   pod/calico-node-j475n                          1/1     Running       0          5m9s
kube-system   pod/calico-node-lnfrf                          1/1     Running       0          4m45s
kube-system   pod/calico-node-pzp7x                          1/1     Running       0          5m
kube-system   pod/coredns-5c98d7d4d8-bg9pl                   1/1     Running       0          12m
kube-system   pod/konnectivity-agent-548hp                   1/1     Running       0          4m45s
kube-system   pod/konnectivity-agent-66cr8                   1/1     Running       0          4m49s
kube-system   pod/konnectivity-agent-lxt9z                   1/1     Running       0          4m58s
kube-system   pod/kube-proxy-ct6bg                           1/1     Running       0          5m
kube-system   pod/kube-proxy-hg8t2                           1/1     Running       0          4m45s
kube-system   pod/kube-proxy-vghs9                           1/1     Running       0          5m9s