K3s

Installation

• Disable swap memory

  • comment swap.img in /etc/fstab

  • swapoff -a

• sudo curl -sfL https://get.k3s.io | sh -

  • By default: service cidr: 10.43.0.0/16 and pod cidr: 10.42.0.0/16

  • to change it, add --cluster-cidr=10.0.0.0/16 --service-cidr=10.1.0.0/16 to above command

• Join Master Node from agent node:

  • sudo cat /var/lib/rancher/k3s/server/node-token on your server: get NODE_TOKEN from master node

  • sudo k3s agent --server https://myserver:6443 --token ${NODE_TOKEN}

• Installing and registering at the same time, all below commands have the same result

curl -sfL https://get.k3s.io | INSTALL_K3S_EXEC="agent --server https://k3s.example.com --token mypassword" sh -s -
curl -sfL https://get.k3s.io | INSTALL_K3S_EXEC="agent" K3S_TOKEN="mypassword" sh -s - --server https://k3s.example.com
curl -sfL https://get.k3s.io | K3S_URL=https://k3s.example.com sh -s - agent --token mypassword
curl -sfL https://get.k3s.io | K3S_URL=https://k3s.example.com K3S_TOKEN=mypassword sh -s - # agent is assumed because of K3S_URL

Verification

• systemctl status k3s.service

• systemctl status k3s-agent.service

Uninstallation

• Master Node: /usr/local/bin/k3s-uninstall.sh

• Agent: /usr/local/bin/k3s-agent-uninstall.sh

Ingress-Controller

• K3s uses Traefik as the default Ingress controller

• Traefik Handles Ingress traffic using ports 80 and 443.

• Uses ServiceLB to distribute traffic across nodes.

• Can be customized via HelmChartConfig (/var/lib/rancher/k3s/server/manifests/traefik.yaml).

• To disable traefik, start K3s with --disable=traefik

Troulbeshooting

Service is activiting

# systemctl status k3s
kmaster k3s[66013]: time="2025-06-07T03:42:37Z" level=info msg="Polling for API server readiness: GET /readyz failed: an error on the server>
# kubectl cluster-info
WARN[0000] Unable to read /etc/rancher/k3s/k3s.yaml, please start server with --write-kubeconfig-mode or --write-kubeconfig-group to modify kube config permissions 
error: error loading config file "/etc/rancher/k3s/k3s.yaml": open /etc/rancher/k3s/k3s.yaml: permission denied
# sudo k3s kubectl get nodes
[sudo] password for user: 
E0607 03:48:30.587592   73836 memcache.go:265] "Unhandled Error" err="couldn't get current server API group list: the server is currently unable to handle the request"

• Solution: ensure minimum server requirement is met

Reference

• K3s Installation