Learn how to - Install Kubernetes Cluster on Ubuntu 20.04 using K3s

Felix Williams How to Kubernetes Linux Tutorials April 19, 2023

Learn how to – Install Kubernetes Cluster on Ubuntu 20.04 using K3s.

Kubernetes is a container orchestration tool for hybrid cloud platforms. It was designed by Google. Kubernetes allows users to manage docker containers across different cloud and virtualization platforms. K3s is a lightweight kubernetes deployment binary that is meant to reduce the ‘heavily loaded’ k8s deployment. K3s is being developed by Rancher.

In this post we shall cover how to install a Kubernetes cluster on Ubuntu 20.04 LTS using k3s. You can check out how to install k8s on Ubuntu 20.04 with kubeadm for an alternative.

Kubernetes architecture involves a Master node and Worker Nodes. Their functions are as follows:

Master – controls the cluster, API calls, e.t.c.
Workers – these handles the workloads, where the pods are deployed and applications ran. They can be added and removed from the cluster.

So to setup a k3s cluster you need at least two hosts, the master node and one worker node. In this post we shall be using one master node and two worker nodes.

We need to prepare our hosts to be able to run k3s in a cluster. Use the following steps to install k3s cluster on Ubuntu 20.04:

Step 1: Update Ubuntu system

With your servers installed with Ubuntu 20.04, update and upgrade them:

sudo apt update
sudo apt -y upgrade && sudo systemctl reboot

Step 2: Map the hostnames on each node

Make sure you have the hostnames mapped on each node. This is by adding the IP and hostname of each node in the /etc/hosts file of each host.

In our setup, it is as follows:

$ sudo vim /etc/hosts
172.16.10.3 master
172.16.10.4 worker01
172.16.10.10 worker02

This has to be done on all the hosts for you to use DNS names.

Step 3: Install Docker on Ubuntu 20.04

The next step is to install docker on on the hosts. As discussed before, Kubernetes is used to manage Docker containers on hybrid cloud infrastructure. Thus we need to have docker up and running on all the nodes before we can setup K3s.

Add Docker APT repository:

sudo apt update
sudo apt install apt-transport-https ca-certificates curl software-properties-common -y
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu focal stable"

Install Docker CE on Ubuntu 20.04:

sudo apt update
sudo apt install docker-ce -y

This has to be done on all the hosts including the master node. After successful installation, start and enable the service.

sudo systemctl start docker
sudo systemctl enable docker

You can also check if the service is started and is running:

$ systemctl status docker
● docker.service - Docker Application Container Engine
     Loaded: loaded (/lib/systemd/system/docker.service; enabled; vendor preset: enabled)
     Active: active (running) since Fri 2020-10-30 08:30:39 CET; 19s ago
TriggeredBy: ● docker.socket
       Docs: https://docs.docker.com
   Main PID: 9275 (dockerd)
      Tasks: 8
     Memory: 35.6M
     CGroup: /system.slice/docker.service
             └─9275 /usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

Oct 30 08:30:39 ubuntu dockerd[9275]: time="2020-10-30T08:30:39.460569874+01:00" level=warning msg="Your kernel does not support cgroup rt runtime"
Oct 30 08:30:39 ubuntu dockerd[9275]: time="2020-10-30T08:30:39.460672730+01:00" level=warning msg="Your kernel does not support cgroup blkio weight"
Oct 30 08:30:39 ubuntu dockerd[9275]: time="2020-10-30T08:30:39.460820506+01:00" level=warning msg="Your kernel does not support cgroup blkio weight_device"
Oct 30 08:30:39 ubuntu dockerd[9275]: time="2020-10-30T08:30:39.461286028+01:00" level=info msg="Loading containers: start."
Oct 30 08:30:39 ubuntu dockerd[9275]: time="2020-10-30T08:30:39.620849970+01:00" level=info msg="Default bridge (docker0) is assigned with an IP address 172.17.0>
Oct 30 08:30:39 ubuntu dockerd[9275]: time="2020-10-30T08:30:39.717281156+01:00" level=info msg="Loading containers: done."
Oct 30 08:30:39 ubuntu dockerd[9275]: time="2020-10-30T08:30:39.754253372+01:00" level=info msg="Docker daemon" commit=4484c46d9d graphdriver(s)=overlay2 version>
Oct 30 08:30:39 ubuntu dockerd[9275]: time="2020-10-30T08:30:39.755461813+01:00" level=info msg="Daemon has completed initialization"
Oct 30 08:30:39 ubuntu systemd[1]: Started Docker Application Container Engine.

Add your user to Docker group to avoid typing sudo everytime you run docker commands.

sudo usermod -aG docker ${USER}
newgrp docker

Step 4: Setup the Master k3s Node

In this step, we shall install and prepare the master node. This involves installing the k3s service and starting it.

curl -sfL https://get.k3s.io | sh -s - --docker

Run the command above to install k3s on the master node. The script installs k3s and starts it automatically.

[INFO]  Finding release for channel stable
[INFO]  Using v1.26.4+k3s1 as release
[INFO]  Downloading hash https://github.com/k3s-io/k3s/releases/download/v1.26.4+k3s1/sha256sum-amd64.txt
[INFO]  Downloading binary https://github.com/k3s-io/k3s/releases/download/v1.26.4+k3s1/k3s
[INFO]  Verifying binary download
[INFO]  Installing k3s to /usr/local/bin/k3s
[INFO]  Creating /usr/local/bin/kubectl symlink to k3s
[INFO]  Creating /usr/local/bin/crictl symlink to k3s
[INFO]  Skipping /usr/local/bin/ctr symlink to k3s, command exists in PATH at /usr/bin/ctr
[INFO]  Creating killall script /usr/local/bin/k3s-killall.sh
[INFO]  Creating uninstall script /usr/local/bin/k3s-uninstall.sh
[INFO]  env: Creating environment file /etc/systemd/system/k3s.service.env
[INFO]  systemd: Creating service file /etc/systemd/system/k3s.service
[INFO]  systemd: Enabling k3s unit
Created symlink /etc/systemd/system/multi-user.target.wants/k3s.service → /etc/systemd/system/k3s.service.
[INFO]  systemd: Starting k3s

To check if the service installed successfully, you can use:

$ systemctl status k3s
● k3s.service - Lightweight Kubernetes
     Loaded: loaded (/etc/systemd/system/k3s.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2023-05-09 13:01:03 UTC; 1min 9s ago
       Docs: https://k3s.io
    Process: 11151 ExecStartPre=/sbin/modprobe br_netfilter (code=exited, status=0/SUCCESS)
    Process: 11152 ExecStartPre=/sbin/modprobe overlay (code=exited, status=0/SUCCESS)
   Main PID: 11153 (k3s-server)
      Tasks: 0
     Memory: 420.9M
     CGroup: /system.slice/k3s.service
             └─11153 /usr/local/bin/k3s server --docker

Oct 30 08:33:32 ubuntu k3s[11153]: I1030 08:33:32.532935   11153 reconciler.go:196] operationExecutor.UnmountVolume started for volume "helm-traefik-token-dmfz6">
Oct 30 08:33:32 ubuntu k3s[11153]: I1030 08:33:32.533481   11153 reconciler.go:196] operationExecutor.UnmountVolume started for volume "values" (UniqueName: "kub>
Oct 30 08:33:32 ubuntu k3s[11153]: W1030 08:33:32.533849   11153 empty_dir.go:453] Warning: Failed to clear quota on /var/lib/kubelet/pods/d1fae0b1-f3ac-481a-b6a>
Oct 30 08:33:32 ubuntu k3s[11153]: I1030 08:33:32.538649   11153 operation_generator.go:782] UnmountVolume.TearDown succeeded for volume "kubernetes.io/configmap>
Oct 30 08:33:32 ubuntu k3s[11153]: I1030 08:33:32.555370   11153 operation_generator.go:782] UnmountVolume.TearDown succeeded for volume "kubernetes.io/secret/d1>
Oct 30 08:33:32 ubuntu k3s[11153]: I1030 08:33:32.653113   11153 reconciler.go:319] Volume detached for volume "helm-traefik-token-dmfz6" (UniqueName: "kubernete>
Oct 30 08:33:32 ubuntu k3s[11153]: I1030 08:33:32.653137   11153 reconciler.go:319] Volume detached for volume "values" (UniqueName: "kubernetes.io/configmap/d1f>
Oct 30 08:33:33 ubuntu k3s[11153]: W1030 08:33:33.978774   11153 pod_container_deletor.go:77] Container "23d34e0acde3f4ab7e41d99e9cff16e7ba8cd76122158dfc18b64ae0>
Oct 30 08:33:33 ubuntu k3s[11153]: W1030 08:33:33.997821   11153 pod_container_deletor.go:77] Container "a52fe91aa3e7b137ebe4dd993e358c382f96b5df342cb1c098acadb6>
Oct 30 08:33:35 ubuntu k3s[11153]: W1030 08:33:35.022454   11153 pod_container_deletor.go:77] Container "2b9f302427059276bc2e1d012db5cbcaeb72ed373cb52218edb6eb4b

You can check if the master node is working by :

sudo kubectl get nodes -o wide

The output should be something like this:

root@mastre:~# sudo kubectl get nodes -o wide
NAME     STATUS   ROLES    AGE    VERSION        INTERNAL-IP     EXTERNAL-IP   OS-IMAGE             KERNEL-VERSION     CONTAINER-RUNTIME
master   Ready    master   3m2s   v1.18.9+k3s1   172.16.10.3   <none>        Ubuntu 20.04.1 LTS   5.4.0-52-generic   docker://19.3.8

Step 5: Allow ports on firewall

We need to allow ports that will will be used to communicate between the master and the worker nodes. The ports are 443 and 6443.

sudo ufw allow 6443/tcp
sudo ufw allow 443/tcp

You need to extract a token form the master that will be used to join the nodes to the master.

On the master node:

sudo cat /var/lib/rancher/k3s/server/node-token

You will then obtain a token that looks like:

K1078f2861628c95aa328595484e77f831adc3b58041e9ba9a8b2373926c8b034a3::server:417a7c6f46330b601954d0aaaa1d0f5b

Step 6: Install k3s on worker nodes and connect them to the master

The next step is to install k3s on the worker nodes. Run the commands below to install k3s on worker nodes:

curl -sfL http://get.k3s.io | K3S_URL=https://<master_IP>:6443 K3S_TOKEN=<join_token> sh -s - --docker

Where master_IP is the IP of the master node and join_token is the token obtained from the master. e.g:

curl -sfL http://get.k3s.io | K3S_URL=https://172.16.10.3:6443 K3S_TOKEN=K1078f2861628c95aa328595484e77f831adc3b58041e9ba9a8b2373926c8b034a3::server:417a7c6f46330b601954d0aaaa1d0f5b sh -s - --docker

You can verify if the k3s-agent on the worker nodes is running by:

sudo systemctl status k3s-agent

To verify that our nodes have successfully been added to the cluster, run :

sudo kubectl get nodes

Your output should look like:

root@master:~# kubectl get nodes -o wide
NAME       STATUS   ROLES    AGE   VERSION        INTERNAL-IP     EXTERNAL-IP   OS-IMAGE             KERNEL-VERSION       CONTAINER-RUNTIME
master     Ready    master   14m   v1.26.4+k3s1  172.16.10.3   <none>        Ubuntu 20.04.1 LTS   5.4.0-52-generic     docker://23.0.6
worker02   Ready    <none>   90s   v1.26.4+k3s1   172.16.10.10   <none>        Ubuntu 20.04.1 LTS   5.4.0-52-generic     docker://23.0.6
worker01   Ready    <none>   41s   v1.26.4+k3s1   172.16.10.4   <none>        Ubuntu 18.04.5 LTS   4.15.0-122-generic   docker://23.0.6

This shows that we have successfully setup our k3s cluster ready to deploy applications to it.

Step 7: Deploy Addons to K3s

K3s is a lightweight kubernetes tool that doesn’t come packaged with all the tools but you can install them separately.

Install Helm Commandline tool on k3s

Download the latest version of Helm commandline tool from this page.
Extract the tar file using tar -xvcf <downloaded-file>
Move the binary file to /usr/local/bin/helm

sudo mv linux-amd64/helm /usr/local/bin/helm

Check version

$ helm version

Add the helm chart repository to allow installation of applications using helm:

helm repo add stable https://charts.helm.sh/stable
helm repo update

Step 8: Deploy an application on k3s

We can now deploy a test application on the K3s cluster.

Deploy Nginx Web-proxy on K3s

Nginx can be used as a web proxy to expose ingress web traffic routes in and out of the cluster.

We can install nginx web-proxy using Helm:

helm install nginx-ingress stable/nginx-ingress --namespace kube-system 
  --set defaultBackend.enabled=false

We can test if the application has been installed by:

$ kubectl get pods -n kube-system -l app=nginx-ingress -o wide

The output should be like:

root@master:~# kubectl get pods -n kube-system -l app=nginx-ingress -o wide
NAME                                       READY   STATUS    RESTARTS   AGE   IP          NODE       NOMINATED NODE   READINESS GATES
nginx-ingress-controller-56547fb57-vsjdm   1/1     Running   0          28s   10.42.2.6   worker01   <none>           <none>

We have successfully deployed nginx web-proxy on k3s.

Install Kubernetes Cluster on Ubuntu 20.04 using K3s 1

Step 9: Removing k3s (Bonus)

To remove k3s on the worker nodes, execute:

sudo /usr/local/bin/k3s-agent-uninstall.sh
sudo rm -rf /var/lib/rancher

To remove k3s on the master node, execute:

sudo /usr/local/bin/k3s-uninstall.sh
sudo rm -rf /var/lib/rancher

Conclusion

In this article, we have been able to deploy k3s on a self hosted environment. We have also deployed helm and nginx on our k3s cluster.

You can find more articles on Kubernetes below:

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Learn how to – Install Kubernetes Cluster on Ubuntu 20.04 using K3s