This tutorial will be a brief walk through the process of getting K3s up and running on Raspberry Pi.

K3s (by RancherLab) and MicroK8s (by Canonical) are the two most popular lightweight Kubernetes for IoT an Edge computing in the industry today. I have used both and I found K3s easier to setup with more advanced configurations for High Availability via an Infrastructure-as-Code automation.

What you’ll learn

Deploying K3s Kubernetes on Raspberry Pi using Ansible
Expose the Kubernetes Service to the public internet

What you’ll need

Components: Please refer to the first blog post in this series
Prepared RPis : Please refer to the second blog post in this series

Why Ansible?

Ansible is an open-source software provisioning, configuration management, and application-deployment tool enabling infrastructure as code. We will use Ansible to install K3s on the master and worker nodes. Ansible will enable you to reset the entire configuration should you need to, or add more nodes to the cluster.

Ansible installation is simple. You can either install it via pip, like this:

python3 -m pip install
or
brew install ansible.

If you’re on the Mac. Although the pip option is the recommended method.

Installing K3s on Raspberry Pi

Rancher has an Ansible playbook that builds a Kubernetes cluster with K3s. Let’s set it up!

Download the Ansible playbook to your Ansible control node - https://github.com/k3s-io/k3s-ansible/archive/master.zip
Duplicate the inventory/sample directory to create an inventory for your RPis, that is :

cp -r inventory/sample inventory/pi

Change the working directory to inventory/pi and edit the hosts.ini file, as shown below:

   [master]
   192.168.master.ip.address

   [node]
   192.168.worker.node.1.ip.address
   192.168.worker.node.2.ip.address
   192.168.worker.node.n.ip.address

   [master:vars]
   ansible_ssh_private_key_file=~/pi
   [node:vars]
   ansible_ssh_private_key_file=~/pi

   [k3s_cluster:children]
   master
   node

Edit the inventory/group_vars/all.yml file and change the ansible_user to pi. You may move the ansible_ssh_private_key_file from hosts.ini into the group vars too if you prefer - assuming you’re using the same key for all.
Still in inventory/group_vars/all.yml, edit k3s_version with the latest version: To get the latest version:
- Navigate to: https://github.com/k3s-io/k3s/tags
- Click the latest release, then copy the last URL segment, for example: v1.20.4%2Bk3s1 is the last URL segment of https://github.com/k3s-io/k3s/releases/tag/v1.20.4%2Bk3s1
In summary, your inventory/group_vars/all.yml should look like this:
```
   ---
   k3s_version: v1.20.4%2Bk3s1 # update this 
   ansible_user: pi # update this too 
   systemd_dir: /etc/systemd/system
   master_ip: ''
   extra_server_args: ""
   extra_agent_args: ""
```
Run it!

ansible-playbook site.yml -i inventory/pi/hosts.ini

Connect to the Cluster

Once it’s built, you need to get the kubectl configuration from the master to connect to the cluster:

scp -i ~/pi pi@pimaster:~/.kube/config ~/.kube/pi-config

Note: The purpose of using ~/.kube/pi-config is to preserve your previous configurations, if any

Next, edit bash_rc or bash_profile by adding this line:

#K8S
export KUBECONFIG=$KUBECONFIG:~/.kube/config:~/.kube/pi-config

Then reload source ~/.bash_profile

Change context

Next, rename the context from default, since you may have a default context already.

kubectl --kubeconfig=~/.kube/pi-config config rename-context default pi

Alternatively, edit ~/.kube/pi-config and change the cluster and context names from default to pi respectively.

Then switch context:

kubectl config get-contexts #list contexts
kubectl config use-context pi  #switch contexts

Well done!

~ $ k get nodes
NAME          STATUS   ROLES                  AGE   VERSION
pinasworker   Ready    <none>                 24d   v1.20.2-rc1+k3s1
pimaster      Ready    control-plane,master   24d   v1.20.2-rc1+k3s1
piworker1     Ready    <none>                 24d   v1.20.2-rc1+k3s1

Exposing your service

To expose your Service to the world, you may consider using a combination of NodePort or MetalB and Port forwarding configuration in your router.
Or
The Inlets operator

SSL

You will need an SSL certificate if you intend to expose your Kubernetes service to the public. You may generate free SSL certificates using https://letsencrypt.org

Troubleshooting

Running kubectl commands from pi master gave me this error.

pi@pimaster:~ $ kubectl get po
WARN[2021-01-14T22:33:39.735790976Z] Unable to read /etc/rancher/k3s/k3s.yaml, please start server with --write-kubeconfig-mode to modify kube config permissions
error: error loading config file "/etc/rancher/k3s/k3s.yaml": open /etc/rancher/k3s/k3s.yaml: permission denied