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K3s part 2: Create a single node cluster

published updated tags k3s

To start testing with k3s, keep it simple, only create one node. You can add more nodes later. You can deploy it anywhere you like, just follow the documentation. Abbreviated notes are below for generic hosts, and detailed instructions for DigitalOcean droplets.

Install k3s on a generic host

If you already have a provisioned Linux server, or Virtual Machine, you can install k3s on it, with a single command.

Before installing, you should know that pods will store data in volumes created in the directory /var/lib/rancher/k3s/storage. You should create this directory prior to install, and optionally mount whatever storage volume you want to have available, on that path. Otherwise, this directory will live on the root filesystem, which might be too small.

You need to add options to the k3s installer command, so as to not start Traefik. Traefik will be installed later by yourself, using an updated version, rather than the one that is bundled with k3s. The k3s installer command is:

## Example k3s install command to run on any server:
curl -sfL https://get.k3s.io | sh -s - server --disable traefik

You can also use k3sup from your workstation, to install k3s on any machine you have SSH access to, and this will automatically download the key to your workstation:

SSH_IP_ADDRESS=x.x.x.x
KUBE_CONFIG=${HOME}/.kube/config
[bash]: Run this on your workstation:
mkdir -p ${HOME}/.kube
k3sup install --ip ${SSH_IP_ADDRESS} --local-path ${KUBE_CONFIG} \
  --k3s-extra-args '--disable traefik'

Create k3s Droplet on DigitalOcean

  • Create a Debian (10 x64) droplet on DigitalOcean
    • $20/mo 4GB RAM (tested configuration, 2GB might work minimally.)
    • Optional: Add a block storage volume for pod data.
      • You choose how much space you need for all of your pods.
      • If you don’t add a volume, pod storage will live on the root filesystem of the droplet. (/var/lib/rancher/k3s/storage)
    • Enter the following script into the User data section of the droplet creation screen:
#!/bin/bash
VOLUME=/dev/sda
mkdir -p /var/lib/rancher/k3s/storage
umount ${VOLUME}
if (blkid ${VOLUME}); then
  yes | mkfs.ext4 ${VOLUME}
  echo "${VOLUME} /var/lib/rancher/k3s/storage " \
       "ext4 defaults,nofail,discard 0 0" | sudo tee /etc/fstab
  mount ${VOLUME}
fi
apt-get update -y
apt-get install -y curl ufw

## UFW firewall rules
ufw allow 22/tcp
ufw allow 80/tcp
ufw allow 443/tcp
ufw allow 6443/tcp
ufw allow 2222/tcp
ufw enable
systemctl enable --now ufw

## k3s install
curl -sfL https://get.k3s.io | sh -s - server --disable traefik
cat /etc/rancher/k3s/k3s.yaml | \
  sed "s/127.0.0.1/$(hostname -I | cut -d ' ' -f 1)/g" \
    > /etc/rancher/k3s/k3s.external.yaml && \
  chmod 0600 /etc/rancher/k3s/k3s.external.yaml

  • Assign your workstation’s ssh client key to the droplet, to allow remote management. Click New SSH Key if you haven’t uploaded one yet.

  • Choose a hostname, like k3s-flux.

  • Confirm the details and click Create Droplet.

  • Note that the script has already installed k3s for you, and mounted the storage volume, so you don’t need to do anything else on the server, it’s ready to go.

  • Assign a floating IP address to your new droplet.

  • Create wildcard DNS names pointing to your droplet’s floating IP address (*.k3s.example.com). To use that link, requires that your domain uses DigitalOcean nameservers, tied to your account. Alternatively, you may set this up with any DNS provider that you use instead.

Download Cluster API Key

To access the cluster from your workstation, you must download the API key from the k3s server. If you used k3sup to create your cluster, you can skip this, k3sup did it for you. Otherwise, set a temporary variable for the the floating IP address of the server, and the desired path to store the cluster key.

FLOATING_IP=X.X.X.X
export KUBECONFIG=${HOME}/.kube/config

Download the key from the cluster. If you installed on DigitalOcean this will work for you:

[bash]: Run this on your workstation:
mkdir -p ${HOME}/.kube
ssh ${FLOATING_IP} -l root -o StrictHostKeyChecking=no \
  cat /etc/rancher/k3s/k3s.external.yaml > ${KUBECONFIG}

(If you installed to a generic host, you must copy /etc/rancher/k3s/k3s.yaml from the server, to your client, and edit the 127.0.0.1 IP address replacing it to be the public IP address of the server node, NOT the floating IP, which the cluster key is not signed for.)

  • Test kubectl access with the key:
[bash]: Run this on your workstation:
 kubectl get node -o wide

(It should print the node status as Ready once k3s finishes initialization. The name of the node displayed, should be the same hostname you created on the droplet page.)

If you set KUBECONFIG to anything other than the default ($HOME/.kube/config) you should add it to your ~/.bashrc file.

export KUBECONFIG=${HOME}/.kube/config
// settings
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