Quickly setup a K3s cluster in one minute using k3sup

Addo Zhang
5 min readOct 27, 2023
Photo by Pixabay from Pexels

Background

In my daily work, in order to facilitate testing in a pure environment, I often need to frequently build and destroy clusters in local or public cloud environments. Sometimes in my HomeLab environment, although the CPU is not powerful, it is better because the memory is large enough. Later, after I got the Azure credit given by Microsoft MVP, I would often set up in Azure virtual machines because there was no network problem of pulling the image. .

In both environments, I used Terraform to quickly create and destroy virtual machines, and then created K3s clusters on the virtual machines. K3s cluster is lightweight enough and supports customization of components. Combined with Alfred Snippets, I only need to ssh to the virtual machine and type k3si to quickly enter customized commands, and then obtain the kubeconfig file on the virtual machine and replace the api in it -server addresses (these are also resolved via snippet):

export MASTER_IP=${MASTER_IP:-$(ip addr show eth0 | grep 'inet ' | awk '{print $2}' | cut -d/ -f1)}
export INSTALL_K3S_VERSION=v1.23.8+k3s1
curl -sfL https://get.k3s.io | sh -s - --disable traefik --disable local-storage --disable metrics-server --advertise-address=$MASTER_IP --disable servicelb --write-kubeconfig-mode 644 --write-kubeconfig ~/.kube/config

A single-node cluster is quite convenient to operate, but when you need a multi-node cluster, you still need to ssh to all hosts for operation. Of course, you need to copy the token of the master node. It’s still a bit cumbersome.

Then I discovered a faster tool, k3sup (pronounced ‘ketchup’) created by Alex Ellis.

Introduction to k3sup

k3sup is a lightweight tool used to quickly build K3s clusters.

k3sup features ease of use, requiring only a single command to install K3s on different platforms. It enables users to quickly create Kubernetes clusters and easily join new nodes to existing clusters.

k3sup connects to the target server via SSH and automatically installs and configures K3s. This means we can install and run Kubernetes on any machine that can be accessed via SSH, including local machines, cloud servers, or devices like Raspberry Pi.

A simple understanding is that k3sup is used to complete a series of operations such as ssh to the host, install K3s server, copy token, ssh to the agent host, install K3s agent… etc.

Next we look at how to use k3sup.

Install k3sup

k3sup is a command line tool. You need to download and install the CLI before using it.

Linux:

curl -sLS https://get.k3sup.dev | sh
sudo install k3sup /usr/local/bin/

macOS:

brew install k3sup

Usage

k3sup supports the following commands:

  • completion:Generates an autocomplete script for the specified shell
  • help:Help
  • install:Install K3s on the server via SSH
  • join:Install the K3s agent on the remote host and join it to the existing cluster
  • ready:Use kubectl to check whether the cluster is ready.
  • update:Print update instructions
  • version:print version

Creating a cluster will use the install and join commands.

Install

The install command is used to install K3s on the server. Use the following command to install k3s on the remote host.

Where --ip points to the address of the remote host, --user is the username to log in to the remote host, --k3s-channel is the version to be installed, --local-path The local storage address of the cluster kubeconf. More options can be viewed via k3sup help install .

k3sup uses ssh key ~/.ssh/id_rsa by default to access the host, which can be specified through the --ssh-key option.

export MASTER_IP=192.168.1.11
k3sup install --ip $MASTER_IP \
--user addo \
--k3s-channel v1.24 \
--local-path /tmp/config

Executing the command will print the logs during the installation process.

Running: k3sup install
2023/10/26 09:04:35 192.168.1.11
Public IP: 192.168.1.11
[INFO] Finding release for channel v1.24
[INFO] Using v1.24.17+k3s1 as release
...
Saving file to: /tmp/config
# Test your cluster with:
export KUBECONFIG=/tmp/config
kubectl config use-context default
kubectl get node -o wide

Execute the command to view node information.

export KUBECONFIG=/tmp/config
kubectl get node -o wide
NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME
master Ready control-plane,master 1m v1.24.17+k3s1 10.0.2.4 <none> Ubuntu 20.04.6 LTS 5.15.0-1047-azure containerd://1.7.3-k3s1

If you are installing a single-node cluster, the install command is sufficient. If it is a multi-node cluster, you also need to use the join command.

Join

Use the join command to initialize the agent node and add it to the current cluster. You need to use --server-ip to specify the IP address of the server node. You also need to specify --k3s-channel The installed version, it is strongly recommended to install the same version on the server node.

export AGENT_IP=192.168.1.12
k3sup join --ip $AGENT_IP --user addo --server-ip $MASTER_IP --k3s-channel v1.24
Running: k3sup join
Agent: 192.168.1.11 Server: 192.168.1.12
Received node-token from 192.168.1.11.. ok.
[INFO] Finding release for channel v1.24
[INFO] Using v1.24.17+k3s1 as release
...

Check nodes:

kubectl get no 
NAME STATUS ROLES AGE VERSION
node-1 Ready <none> 43s v1.24.17+k3s1
master Ready control-plane,master 2m58s v1.24.17+k3s1

Full Scripts

With the help of ChatGPT, generate a script to create a cluster with one click. You can try how long it takes to create a two-node cluster. I tried it and it took about 32 seconds.

# Define IP addresses
export HOSTS="192.168.1.11 192.168.1.12"

Setup Cluster

#!/bin/bash

# Read the list of IP addresses from the environment variable
IP_ADDRESSES=($HOSTS)
# Define the k3s version
K3S_VERSION="v1.24"

# Check if there is at least one IP address
if [ ${#IP_ADDRESSES[@]} -eq 0 ]; then
echo "No IP addresses found. Please ensure the HOSTS environment variable is correctly set."
exit 1
fi

# Install the master node
MASTER_IP=${IP_ADDRESSES[0]}
echo "Installing master node: $MASTER_IP"
k3sup install --ip $MASTER_IP --user addo --k3s-channel $K3S_VERSION \
--k3s-extra-args '--write-kubeconfig-mode 644 --write-kubeconfig ~/.kube/config --disable traefik --disable metrics-server --disable local-storage --disable servicelb' \
--local-path /tmp/config

# Install the other agent nodes
for i in "${!IP_ADDRESSES[@]}"; do
if [ $i -ne 0 ]; then
AGENT_IP=${IP_ADDRESSES[$i]}
echo "Installing agent node: $AGENT_IP"
k3sup join --ip $AGENT_IP --server-ip $MASTER_IP --user addo --k3s-channel $K3S_VERSION
fi
done

echo "k3s cluster installation complete."

Cleanup Cluster

#!/bin/bash

# Read the list of IP addresses from the environment variable
IP_ADDRESSES=($HOSTS)
# Check if there is at least one IP address
if [ ${#IP_ADDRESSES[@]} -eq 0 ]; then
echo "No IP addresses found. Please ensure the HOSTS environment variable is correctly set."
exit 1
fi
# Clean up the master node
MASTER_IP=${IP_ADDRESSES[0]}
echo "Cleaning up master node: $MASTER_IP"
ssh -i ~/.ssh/id_rsa $MASTER_IP k3s-uninstall.sh
# Clean up the other agent nodes
for i in "${!IP_ADDRESSES[@]}"; do
if [ $i -ne 0 ]; then
AGENT_IP=${IP_ADDRESSES[$i]}
echo "Cleaning up agent node: $AGENT_IP"
ssh -i ~/.ssh/id_rsa $AGENT_IP k3s-agent-uninstall.sh
fi
done
echo "k3s cluster cleanup complete."

--

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Addo Zhang

CNCF Ambassador | LF APAC OpenSource Evangelist | Microsoft MVP | SA and Evangelist at https://flomesh.io | Programmer | Blogger | Mazda Lover | Ex-BBer