Monday, January 4, 2021

Notes from installing K3s on my Raspberry Pi cluster...

I put a Raspberry Pi cluster together  - now what should I do?

I have a problem when it comes to Raspberry Pis. Actually, I have a problem with impulsivity, but I'll pretend that the issue is exclusive to Raspberry Pis. The great thing is that the cost of the various Raspberry Pi models is low enough that it's relatively cheap to build a cluster. 

I knew I wanted to do the following:

  • Learn more about Kubernetes without using work resources.
  • Try some of the very neat open source projects that are mentioned on the Kubernetes podcast (ie, OpenFaas, MinIO, etc).
  • Play around with some DIY home automation. I'm not completely sure what I want to do yet, but I have a bunch of Philips Hue lights that are begging to be controlled from the cluster.

I did a search for "Raspberry Pi cluster" and "Kubernetes", and found Jeff Geerling's Raspberry Pi Cluster Ep 2 - Setting up the Cluster YouTube video.

Jeff's Kubernetes and Raspberry Pi videos are packed with useful information and he communicates very clearly. Definitely check them out!

I mostly followed his related blog post when I went to install K3s on my cluster. The K3s site has great information as well, and the install steps (all two of them) are very simple to follow. 

However, I ran into an issue or two when I was first setting up the cluster, so I took some notes that I'm providing here. 

Initial OS Selection and Setup

I used Raspberry Pi OS Lite from the Raspberry Pi OS Download page.

Jeff's blog post lists steps for how to copy the Raspberry Pi OS image onto the SD cards, so I'll leave those steps out. However, before I unmounted the SD card I copied the following text to the /boot/cmdline.txt file:

cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory

On First Boot

I made the following changes on first boot of each image:

  1. Changed the password
  2. sudo apt-get update && sudo apt-get upgrade -y && sudo apt-get install -y vim
  3. Set the hostname. I named my Raspberry Pis so they matched my network cable colors, so I ran a command similar to this: echo -e "green" | sudo tee /etc/hostname
  4. Set locale, timezone, and WLAN channel country via raspi-config
  5. Updated raspi-config
  6. Changed memory available to the GPU to 16 MB (A3 Memory Split)
  7. Expanded the file system to max size available

There is (or was) an issue with Raspberry Pi OS Lite (Raspbian Buster) from a recent update, and the cgroup info that is added to /boot/cmdline.txt was being ignored. The work-around is to run a raspberry pi update.


Before Installing K3s

There is a section on where it shows that if you are using Raspian Buster (which is Raspberry Pi OS Lite) then you should enable legacy iptables:

sudo iptables -F
sudo update-alternatives --set iptables /usr/sbin/iptables-legacy
sudo update-alternatives --set ip6tables /usr/sbin/ip6tables-legacy
sudo reboot

I ran the following on each of the Raspberry Pis:

echo -e "\twhite" | sudo tee -a /etc/hosts
echo -e "\tred"   | sudo tee -a /etc/hosts
echo -e "\tgreen" | sudo tee -a /etc/hosts
echo -e "\tblue"  | sudo tee -a /etc/hosts
echo -e "\tblack" | sudo tee -a /etc/hosts

Installing K3s


This will tell the installer that it is a server because the K3S_URL wasn’t set:

curl -sfL | K3S_KUBECONFIG_MODE="644" sh -s -

Get the token from the leader node and trigger the download and execution of the install script. The first Pi in the cluster has a white network cable, so I arbitrarily chose it as the leader node. I ran the following on each of the follower nodes.

export TOKEN=`ssh -t pi@white sudo cat /var/lib/rancher/k3s/server/node-token`
curl -sfL | K3S_URL= K3S_TOKEN=$TOKEN sh -

Test the Cluster

If you haven’t already installed kubectl, then install it now.

Copy the /etc/rancher/k3s/k3s.yaml file from the leader node of your Raspberry Pi cluster, to ~/.kube/config on whatever computer you plan on using to access the cluster. The location might be different on a Windows machine, but that would most likely be the correct path if you’re using the bash shell.

scp pi@white:/etc/rancher/k3s/k3s.yaml ~/.kube/config

Now run kubectl get pods —all-namespaces and see that the cluster already has pods running on the nodes.

Let's Run Something!

I found Alex Ellis's blog post called "Will it cluster?" and followed his instructions for installing OpenFaas. It seems funny now because I had no idea who Alex Ellis was at the time. I only tried OpenFaas because of the "Will it cluster?" blog post. 

I installed OpenFaas, copied the service and deployment yaml files Alex provided in the "Will it cluster?" post, and was able to use the Figlet application in just a few minutes. Very neat stuff!

I recommend going to the site to learn more about using OpenFaas. 

This example shows that sending text to one of the nodes in the cluster (it doesn't matter which node you pick) will run the figlet function - a function that converts your text data into an ASCII art version of the text.

> echo -n "Hello" | curl --data-binary @- http://red:31111
 _   _      _ _
| | | | ___| | | ___
| |_| |/ _ \ | |/ _ \
|  _  |  __/ | | (_) |
|_| |_|\___|_|_|\___/

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