I chose k3s as it incredibly lightweight but still CNCF certified and production grade software that is optimised for resource constraints of raspberry pis.

Pre-requisites

Cluster machines

For this guide I am using three Raspberry Pi 4 4GB machines.

The cluster will have one leader node and two worker nodes. For resiliency puposes in future I will update the cluster to run with two leader nodes.

TODO Migration to high availability control plane

For resiliency purposes in future I will update the cluster and this documentation to support a control plane of more than one machine.

Boot media

This guide requires each Raspberry Pi to have a removable SD card or other removable boot media. I am use three 32GB SD Cards though any USB or SD card at least 8GB in size should work fine.

TODO Migration to network booting

In future it would be preferable for the raspberry pi's to be able to network boot and setup automatically without an SD card.

This is a nice to have that I will pursue at a later date once I have a deployed cluster that allows me to migrate off the current server setup I have deployed.

Step 1 - Prepare boot media for master

Download the latest release

Our first step is to create the bootable SD Card with a minimal install of Raspbian, which is a free operating system based on Debian and is optimised for Raspberry Pi hardware.

Rather than doing an installation and configuration of an operating system image from scratch I found this project on Github which automates the install and configuration process nicely.

echo Downloading latest release zip from github
curl -s https://api.github.com/repos/foodeas/raspberrypi-ua-netinst/releases/latest \
| grep "browser_download_url.*zip" \
| cut -d : -f 2,3 \
| tr -d \" \
| wget -i -

echo Checking file is now present
ls -l | grep *.zip

echo Extracting the zip file
unzip -q -d installer *.zip
ls -l | grep installer

Downloading latest release zip from github
Checking file is now present
-rw-rw-rw- 1 james james 60299545 Aug 12 08:35 raspberrypi-ua-netinst-v2.4.0.zip
Extracting the zip file
drwxrwxrwx 1 james james     4096 Dec 24 19:35 installer
-rw-rw-rw- 1 james james     1351 Dec 24 18:02 installer-config.txt

Apply custom install configuration

Our next step after downloading the latest release is to apply our own installation configuration using a simple txt file.

There is great documentation online howing what configuration options are available here.

For our purposes we just over-write the file downloaded and extracted in the previous step with one we have prepared earlier :)

echo Display wordcount of original file for comparison
wc installer/raspberrypi-ua-netinst/config/installer-config.txt

echo Overwriting /installer/raspberrypi-ua-netinst/config/installer-config.txt
cp installer-config.txt /installer/raspberrypi-ua-netinst/config/

echo Display wordcount of file after copy to validate update
wc installer/raspberrypi-ua-netinst/config/installer-config.txt

Display wordcount of original file for comparison
  33   64 1351 installer/raspberrypi-ua-netinst/config/installer-config.txt
Overwriting /installer/raspberrypi-ua-netinst/config/installer-config.txt
Display wordcount of file after copy to validate update
  33   64 1351 installer/raspberrypi-ua-netinst/config/installer-config.txt

Apply custom post install script

The final step is to supply a post install script which completes additional security hardening and production readiness automatically.

To supply a script we can provide an additional post-install.txt file as documented here.

I have a hardening script prepared in this repository that we can copy in.

echo Copying in post-install.txt
cp post-install.txt /installer/raspberrypi-ua-netinst/config/

echo Display wordcount of file after copy to validate
wc installer/raspberrypi-ua-netinst/config/post-install.txt

Step 2 - Copy the install media to sd card

Our next step is to copy the contents of the installer/ folder to a FAT32 formatted SD Card.

Unfortunately this is currently a windows step as my dev environment is a Windows 10 laptop with Debian via Windows Subsystem for Linux which does not support lsblk or other disk management commands.

Obtain sd card partition information

Our first step is to insert the SD Card and ensure it is formatted correctly as FAT32. To do that we need to know the number of the disk we want to format, we can find that via powershell.

echo Retrieving disk list via powershell
powershell.exe -nologo 
get-disk | select Number, FriendlyName, Size

echo Retrieving partition list via powershell
get-disk | get-partition | select PartitionNumber, DriveLetter, Size, Type
exit

Retrieving disk list via powershell

Number FriendlyName                       Size
------ ------------                       ----
     1 Realtek PCIE Card Reader    31104958464
     0 SAMSUNG MZVLB256HAHQ-000H1 256060514304

Retrieving partition list via powershell

PartitionNumber DriveLetter         Size Type        
--------------- -----------         ---- ----        
              1           D    268435456 FAT32 XINT13
              2           E  30832328704 Unknown     
              1                272629760 System      
              2                 16777216 Reserved    
              3           C 254735810560 Basic       
              4               1027604480 Recovery

Create and format sd card partition

Once we know the number of the disk we want to format we can proceed. In the example above I have a 32GB SD Card which shows as number 1.

Checking the disk we can see some partitions that exist already from previous use of the card. To delete these partitions you can use the Remove-Partition -DiskNumber X -PartitionNumber Y command where X and Y relate to the output of your disk and partition number.

Due to the risk of data loss this step is not automated. Once existing partitions have been cleared we can use the following block to:

Create a new partition using masixmum available space
Assign a free drive letter in windows
Mount the disk in WSL so we can copy to it
Copy the install media over to the partition

echo Use powershell to create new partition and format 
powershell.exe -nologo
new-partition -disknumber 1 -usemaximumsize -driveletter d
format-volume -driveletter d -filesystem FAT32 -newfilesystemlabel sd
exit

echo Mount the new partition in wsl
sudo mkdir /mnt/d
sudo mount -t drvfs d: /mnt/d

echo Copy the contents of installer to sd
cp -r installer/* /mnt/d/

Step 3 - Boot the pi and remotely connect

Provided the configuration on the sd card is valid and the pi has been able to successfully obtain an ip address via dhcp on boot then following a 10-20minute net install process the pi will be online and accessible via ssh using the private key corresponding to the public key we supplied in our installer-config.txt file.

readme.org

Raspberry pi k3s cluster guide