rpi-cluster

• 👨‍💻 Motivation
• 🧰 Hardware
• 🔬 Setting up the microSD card
• 🥾 Setting up USB boot
• 👩‍🍳 Changing the hostname
• 👤 Change user
• 🔑 Set up .pub key authentication
• 📁 SSH config file
• 🚀 Setting up k3s
• 📈 Setting up monitoring tools
• 👨‍🏫 Things I learned

👨‍💻 Motivation

The Pi cluster is a hobby project I work on in my spare time. My primary motivation is to learn, but it’s also just fun. In particular, I would like to learn:

• Kubernetes
• Linux stuff
• Scaling shiny

🧰 Hardware

• MacBook Pro 2019 16" laptop to work with the Pi
• 3 Raspberry Pi’s, 8GB model
• 1 MicroSD card
• 3 USB >= 3.0
• 1 Network switch with 4 PoE ports
• 3 PoE hats
• 3 CAT6 cables
• 1 Cluster case that has 3 layers

🔬 Setting up the microSD card

First step is to configure a microSD card that’s running Raspberry Pi OS. I wont go into detail on how that part is done, check the official imaging tools, it’s a simple process. Additionally, I am not using WiFi at all, so I skip steps like setting up the wpa_supplicant.conf file.

Anyway, after you’ve written the Pi OS to a microSD card enable SSH:

touch /Volumes/boot/ssh

Now unmount the drive, insert it into the Pi and turn it on! If all goes as planned, you can find your Pi’s IP with nmap:

nmap -sn 192.168.1.0/24 # ip may very, check what your ip is

You should see something like “raspberrypi”, identify the IP associated with this and SSH into the device. From here, we can update the EEPROM:

# pw: raspberry
ssh pi@<IP found in above step>

# upgrade eeprom and reboot
sudo apt-get upgrade -y
sudo rpi-eeprom-update -a
sudo reboot

This next step may not be applicable to others but this was the key to get my Pi’s booting from USB (I think, trial and error makes it all this fuzzy). We need to modify the boot order of the Pi’s, I discovered this bit of information from:

• https://jamesachambers.com/new-raspberry-pi-4-bootloader-usb-network-boot-guide/

SSH back in the Pi and run:

# verify that the BOOT_ORDER=0x1 line is changed to BOOT_ORDER=0x4
sudo -E rpi-eeprom-config --edit

# then reboot
sudo reboot

SSH back in the Pi and shut it down for now:

sudo shutdown -h now

We are ready to set up the USB boot!

🥾 Setting up USB boot

Just as the imager tool was used with the microSD, do the same but with Ubuntu Server 20.10 on a USB device. Once this completes, we need to edit some files, I discovered this information from:

• https://github.com/DavidUnboxed/Ubuntu-20.04-WiFi-RaspberyPi4B

We need to edit:

1. user-data
2. network-config

You can reference the repository above, or just reference the code below. For network-config we need something like:

version: 2
ethernets:
  eth0:
    # Rename the built-in ethernet device to "eth0"
    match:
      driver: bcmgenet smsc95xx lan78xx
    set-name: eth0
    dhcp4: true
    optional: true

For user-data we need something like:

#cloud-config

chpasswd:
  expire: true
  list:
  - ubuntu:ubuntu

ssh_pwauth: true

power_state:
  mode: reboot

If I remember correctly, the power_state part was needed to get WiFi working, and I ditched using WiFi entirely, so it may not be needed anymore (assuming you are going ethernet only route).

Now, with the Pi shutdown and disconnected from power, insert the USB and remove the microSD. Turn on the Pi and it should boot from USB now. Repeat this process for all Pi’s.

👩‍🍳 Changing the hostname

For all my Pi’s, I want clear hostnames to organize my cluster. I went with the following naming:

1. main
2. worker-01
3. worker-02

To do this, SSH in the Pi and run:

sudo hostnamectl set-hostname <desired hostname>

Now reboot the device with sudo reboot. Repeat all the stuff with the other Pi’s.

👤 Change user

The default user is ubuntu but I want to change it. In my case, I have a user pirate for all Pi’s. To do this, I ran:

# check groups of ubuntu
groups

# add a user
sudo adduser pirate

# set groups for pirate (i found these groups by running `groups` as you see above)
sudo usermod -a -G adm,dialout,cdrom,floppy,sudo,audio,dip,video,plugdev,netdev,lxd pirate

Log out of the Pi with exit and try to log in with your new username. If you can login with out issue, delete the ubuntu user:

sudo deluser --remove-home ubuntu

🔑 Set up .pub key authentication

I think there are multiple ways you can set up key based authentication, there is a .pem and .pub file, I’m not sure which is better or what the difference is but I’m using .pub. This allows your to SSH into the Pi’s without entering passwords and has a number of other benefits like allowing Ansible to control your Pi cluster. To do this, I start by making a key if you don’t already have one:

ssh-keygen -t rsa -b 4096 -C "tyler@rpi" # put whatever comment you want

Now copy the key to each Pi:

ssh-copy-id -i ~/.ssh/id_rsa.pub pirate@<ip>

Next time you SSH, no password should be required.

📁 SSH config file

Set up a config file in ~/.ssh/ directory to you can assign a name to each connection:

nano ~/.ssh/config

Then add something like:

Host rpi-main
  User pirate
  HostName <ip>

Host rpi-worker-01
  User pirate
  HostName <ip>

Host rpi-worker-02
  User pirate
  HostName <ip>

Now you can SSH into the Pi’s with ssh rpi-main.

🚀 Setting up k3s

I basically followed this:

• https://www.jeffgeerling.com/blog/2020/installing-k3s-kubernetes-on-turing-pi-raspberry-pi-cluster-episode-3

I clone the k3s-ansible project to this repo and removed some stuff I didn’t need, things like the README, and then:

1. Edit inventory/hosts.ini, add node IPs.
2. Edit inventory/group_vars/all.yml and change the ansible_user to pirate.
3. Run ansible-playbook site.yml -i inventory/hosts.ini --ask-become-pass

Now grab the kube config file with:

scp pirate@main:~/.kube/config ~/.kube/config-rpi

If kubectl isn’t installed, brew install kubectl. Set the KUBECONFIG environment variable with:

export KUBECONFIG=~/.kube/config-rpi

If you want this to be permanent, put it in your ~/.zshrc file. After all of this, you should be able to fetch all nodes with kubectl get nodes.

Note, that I think the --ask-become-pass part is not supposed to be necessary. I may have configured things wrong, but adding it allows this playbook to complete.

📈 Setting up monitoring tools

I basically followed this:

• https://www.jeffgeerling.com/blog/2020/raspberry-pi-cluster-episode-4-minecraft-pi-hole-grafana-and-more

And used carlosedp/cluster-monitoring to easily set up monitoring for the Pis. I cloned this repository to my main node and followed the k3s instructions.

👨‍🏫 Things I learned

• I struggled with WiFi on the Pi’s and in the end decided it wasn’t worth the effort. After trial and error, and learning about power_state in the cloud-config, I could get WiFi working on USB but it wasn’t reliable. For example, setting up k3s via Ansible would constantly error out. However, the Ansible playbook just worked after switching to ethernet.

• I struggled with cloud-config, but I want to revisit. In this guide, I have some steps where I set the hostname, copy the SSH key, create a different user, and more. All of this can be handled in the cloud-config file on the first boot of the Pi, but I couldn’t get it working. For example, I couldn’t get hostname or ssh_authorized_keys to work.