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Paul Duplys
Paul Duplys

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À la Carte for Devs: microk8s on Raspberry Pi 4

#kubernetes #raspberrypi #microk8s

After finally getting my hands on a gorgeous Raspberry Pi 4 (the version with 4 GB of RAM), I decided to test-drive it by installing Canonical's microk8s, a small, single-package, CNCF certified fully-conformant upstream Kubernetes deployment for offline development, prototyping, and testing.

It came in handy that I had watched the superb "Docker Mastery: with Kubernetes + Swarm" course by Bret Fisher and so could apply the things I learned there. I can definitely recommend this course if you are interested in learning Docker, Swarm, and Kubernetes from the ground up. Bret is a great instructor and, besides the videos and slides, the course contains a lot of good exercises and handy reference material. All in all, it took me about 2 hours to install everything and maybe another 1 hour to play around a bit and set things up.

In this post, I'll show you step by step how you can replicate that and create a microk8s Kubernetes deployment on your Raspberry Pi 4. This will give you a nice environment where you can quickly deploy any containerized applications to experiment, prototype, test, and play around at home.

The Hardware

In addition to the Raspberry Pi 4 microcomputer itself, you'll need 3 extra hardware items.

  • A power supply for the Raspberry. I use Raspberry Pi 15.3W USB-C, the officially recommended USB-C power supply for Raspberry Pi 4.
  • An microSD card for storing the operating system, Docker + Kubernetes and your applications on your Raspberry. I use a 128GB microSD card from SanDisk.
  • A network cable to connect the Raspberry to your router. Any Ethernet cable will do.

Installing Ubuntu 18.04 on Raspberry Pi 4

First of all, you need to install an operating system on the Raspberry. I chose Ubuntu Server because of its comprehensive package repositories and long-term support (LTS). Shortly after I was preparing this post, Ubuntu switched from 18.04 to 20.04 LTS release, but the instructions given here should work on 20.04 as well.

To get the Ubuntu image for Raspberry Pi, visit the official Ubuntu download website and download the 64-bit version of the Ubuntu Pi image. Follow the installation instructions.

Once the download is complete you need to extract the Ubuntu Server 20.04 image (the .xz file is an archive) and copy it onto your microSD card. The installation instructions contain links to short tutorials on how to do this under Linux, Windows and Macs. If you happen to be on a Windows machine, you can use the win32disk tool to write the Ubuntu image onto the microSD card (remember that you first need unpack the .xz archive).

Because I'm too lazy to use an extra screen for the installation, I rather chose to ssh into the Raspberry Pi once it has booted. To enable this, you can follow the instructions described here and simply create a new file called ssh in the root directory of your microSD card (it's the same directory where files like config.txt are located). This will enable the ssh daemon at the first boot of your Rapsberry so you will be able to immediately ssh into it.

Next, you need connect the Raspberry to your router using a network cable, insert the microSD card into the SD card slot and power up the Raspberry Pi.

Connect to your router - most of them like e.g., the AVM FritzBox have a web admin frontend where you can login; If you happen to have a FritzBox, just fire up your browser and enter http://fritz.box. This will give you a login mask. Once you logged in, look up the IP address of the newly connected Raspberry Pi. Typically, it will have ubuntu as its device name.

Now, from your host (which obviously needs to be connected to the same router, e.g., via WiFi), do:

$ ssh ubuntu@<IP address of your pi>
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and enter ubuntu when asked for password. When logging in for the first time, you will be asked to choose a new password. From then on, you login using the user ubuntu and your new password.

Installing microk8s

To install and use microk8s, you need cgroups. By default, cgroups are not enabled on the Ubuntu server image for Raspberry Pi. As described in this microk8s documentation, you need to edit the boot parameters in nobtcmd.txt (attention: in the older Pi versions before Pi 4, this file was called cmdline.txt; if you google for how to enable cgroups on a Raspberry Pi, you might hit a tutorial that uses this outdated name). Thus, fire up the vi editor as root using sudo:

ubuntu@ubuntu:~$ sudo vi /boot/firmware/nobtcmd.txt
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and add the following line:

cgroup_enable=memory cgroup_memory=1
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After the change, you need to reboot the Raspberry Pi for it to take effect. To do this, issue:

ubuntu@ubuntu:~$ sudo reboot
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Next, follow the instructions on the microk8s website on how to install microk8s using snap. As I'm writing this post, the current channel version is 1.18. So on your Raspberry Pi, issue:

ubuntu@ubuntu:~$ sudo snap install microk8s --classic --channel=1.18/stable
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After the installation is complete, you need to add your current user ubuntu to the microk8s group and make some other changes. See the microk8s documentation for details. You need to do the following:

ubuntu@ubuntu:~$ sudo usermod -a -G microk8s $USER ubuntu@ubuntu:~$ sudo chown -f -R $USER ~/.kube ubuntu@ubuntu:~$ su - $USER Password: ubuntu@ubuntu:~$ microk8s status --wait-ready microk8s is running addons: dashboard: disabled dns: disabled helm: disabled helm3: disabled ingress: disabled kubeflow: disabled metallb: disabled metrics-server: disabled rbac: disabled registry: disabled storage: disabled ubuntu@ubuntu:~$ microk8s kubectl get nodes NAME STATUS ROLES AGE VERSION ubuntu Ready <none> 10m v1.18.0 ubuntu@ubuntu:~$ microk8s kubectl get services NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE kubernetes ClusterIP 10.152.183.1 <none> 443/TCP 10m
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Congrats! You now have a working microk8s installation on your Raspberry Pi 4!

Deploying nginx with microk8s

To play around with your new shiny microk8s installation, you can create a deployment for nginx, a popular HTTP and reverse proxy server. If you want to learn more about nginx, visit their website. Start by creating a Kubernetes deployment using the nginx Docker image and verify that the deployment has been indeed created:

ubuntu@ubuntu:~$ microk8s.kubectl create deployment my-nginx --image nginx deployment.apps/my-nginx created ubuntu@ubuntu:~$ microk8s.kubectl get all NAME READY STATUS RESTARTS AGE pod/my-nginx-9b596c8c4-ngd2q 1/1 Running 0 12m NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE service/kubernetes ClusterIP 10.152.183.1 <none> 443/TCP 47h NAME READY UP-TO-DATE AVAILABLE AGE deployment.apps/my-nginx 1/1 1 1 12m NAME DESIRED CURRENT READY AGE replicaset.apps/my-nginx-9b596c8c4 1 1 1 12m ubuntu@ubuntu:~$ microk8s.kubectl get services NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE kubernetes ClusterIP 10.152.183.1 <none> 443/TCP 47h
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Next, you can optionally increase the number of your replicas (and again verify that it worked):

ubuntu@ubuntu:~$ microk8s.kubectl scale deployment my-nginx --replicas 3 deployment.apps/my-nginx scaled ubuntu@ubuntu:~$ microk8s.kubectl get all NAME READY STATUS RESTARTS AGE pod/my-nginx-9b596c8c4-4jp7d 1/1 Running 0 7s pod/my-nginx-9b596c8c4-7ql2q 1/1 Running 0 7s pod/my-nginx-9b596c8c4-ngd2q 1/1 Running 0 14m NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE service/kubernetes ClusterIP 10.152.183.1 <none> 443/TCP 47h NAME READY UP-TO-DATE AVAILABLE AGE deployment.apps/my-nginx 3/3 3 3 14m NAME DESIRED CURRENT READY AGE replicaset.apps/my-nginx-9b596c8c4 3 3 3 14m
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Finally, you need to expose a so-called NodePort so that the nginx deployment can be accessed from anywhere within your home network using the IP address of your Raspberry Pi. Issue the following commands:

ubuntu@ubuntu:~$ microk8s.kubectl expose deployment my-nginx --port 80 --name my-nginx-np --type NodePort service/my-nginx-np exposed ubuntu@ubuntu:~$ microk8s.kubectl get services NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE kubernetes ClusterIP 10.152.183.1 <none> 443/TCP 47h my-nginx-np NodePort 10.152.183.73 <none> 80:30178/TCP 13s ubuntu@ubuntu:~$ microk8s.kubectl get all NAME READY STATUS RESTARTS AGE pod/my-nginx-9b596c8c4-4jp7d 1/1 Running 0 3m34s pod/my-nginx-9b596c8c4-7ql2q 1/1 Running 0 3m34s pod/my-nginx-9b596c8c4-ngd2q 1/1 Running 0 17m NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE service/kubernetes ClusterIP 10.152.183.1 <none> 443/TCP 47h service/my-nginx-np NodePort 10.152.183.73 <none> 80:30178/TCP 20s NAME READY UP-TO-DATE AVAILABLE AGE deployment.apps/my-nginx 3/3 3 3 17m NAME DESIRED CURRENT READY AGE replicaset.apps/my-nginx-9b596c8c4 3 3 3 17m
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Let's verify that nginx is working and can be accessed using the host IP address, from outside of the Raspberry Pi. To do this, exit your ssh session and from your host machine, do:

$ curl <IP address of your Raspberry Pi>:30178 <!DOCTYPE html> <html> <head> <title>Welcome to nginx!</title> <style> body { width: 35em; margin: 0 auto; font-family: Tahoma, Verdana, Arial, sans-serif; } </style> </head> <body> <h1>Welcome to nginx!</h1> <p>If you see this page, the nginx web server is successfully installed and working. Further configuration is required.</p> <p>For online documentation and support please refer to <a href="http://nginx.org/">nginx.org</a>.<br/> Commercial support is available at <a href="http://nginx.com/">nginx.com</a>.</p> <p><em>Thank you for using nginx.</em></p> </body> </html>
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Congratulations!! You now have a working microk8s deployment and the nginx application up and running on Kubernetes.

Further References

You can also check out these references:

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