How to Install Kubernetes Cluster on Ubuntu 20.04 LTS with kubeadm

In this article we are going to cover How to Install Kubernetes Cluster on Ubuntu 20.04 LTS with kubeadm or any other cloud platform like Amazon EC2, Azure VM, Google Cloud Compute,etc. with preinstalled Ubuntu 20.04 LTS.

Prerequisites

• 2 or 3 Ubuntu 20.04 LTS System with Minimal Installation
• Minimum 2 or more CPU, 3 GB RAM.
• Disable SWAP on All node
• SSH Access with sudo privileges

Firewall Ports/Inbound Traffic Ports for Kubernetes Cluster

Control-plane node(s)

Protocol	Direction	Port Range	Purpose	Used By
TCP	Inbound	6443*	Kubernetes API server	All
TCP	Inbound	2379-2380	etcd server client API	kube-apiserver, etcd
TCP	Inbound	10250	Kubelet API	Self, Control plane
TCP	Inbound	10251	kube-scheduler	Self
TCP	Inbound	10252	kube-controller-manager	Self

Worker node(s)

Protocol	Direction	Port Range	Purpose	Used By
TCP	Inbound	10250	Kubelet API	Self, Control plane
TCP	Inbound	30000-32767	NodePort Services†	All

Disable swap

swapoff -a

sudo sed -i '/ swap / s/^\(.*\)$/#\1/g' /etc/fstab

Also comment out the reference to swap in /etc/fstab. Start by editing the below file:

sudo nano /etc/fstab

Reboot the system to take effect

sudo reboot

Update the system Packages

sudo apt-get update

#1. Install Docker Container Runtime on All node (Master and Worker Nodes)

Install below packages if not installed

sudo apt-get install -y \
    apt-transport-https \
    ca-certificates \
    curl \
    gnupg \
    lsb-release

Add the Docker official GPG Key

curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

Add the Docker APT repository

echo   "deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu \
  $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

Update the System Packages

sudo apt-get update -y

Install docker community edition and container runtime on both master and worker node

sudo apt-get install docker-ce docker-ce-cli containerd.io -y

Add the Docker Daemon configurations to use systemd as the cgroup driver.

cat <<EOF | sudo tee /etc/docker/daemon.json
{
  "exec-opts": ["native.cgroupdriver=systemd"],
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "100m"
  },
  "storage-driver": "overlay2"
}
EOF

Check docker images

docker images

ERROR:

Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Get http://%2Fvar%2Frun%2Fdocker.sock/v1.40/images/json: dial unix /var/run/docker.sock: connect: permission denied

Solution:

Add the docker user in group and give permission for docker.sock

sudo usermod -aG docker $USER

Change the docker.sock permission

sudo chmod 666 /var/run/docker.sock

Start the Docker service if not started

sudo systemctl start docker.service

To check the docker service status

sudo systemctl status docker.service

Enable Docker service at startup

sudo systemctl enable docker.service

Restart the Docker service

sudo systemctl restart docker

#2. Add Kubernetes GPG Key on All node

Add Kubernetes GPG key in all node.

sudo curl -fsSLo /usr/share/keyrings/kubernetes-archive-keyring.gpg https://packages.cloud.google.com/apt/doc/apt-key.gpg

#3. Add Kubernetes APT Repository on All node

Add Kubernetes apt repository on all node for Ubuntu.

echo "deb [signed-by=/usr/share/keyrings/kubernetes-archive-keyring.gpg] https://apt.kubernetes.io/ kubernetes-xenial main" | sudo tee /etc/apt/sources.list.d/kubernetes.list

update the system packages

sudo apt-get update

#4. Install Kubeadm,Kubelet and Kubectl on All Node

Install kubeadm,kubelet and kubectl using below command.

sudo apt-get install -y kubelet kubeadm kubectl

Hold the packages to being upgrade

sudo apt-mark hold kubelet kubeadm kubectl

How to Install Kubernetes Cluster on Ubuntu 20.04 LTS with kubeadm

#5. Initialize the Master node using kubeadm (on Master Node)

Next initialize the master node using kubeadm.

sudo kubeadm init --pod-network-cidr 10.0.0.0/16

Output:

Your Kubernetes control-plane has initialized successfully!

To start using your cluster, you need to run the following as a regular user:

  mkdir -p $HOME/.kube
  sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
  sudo chown $(id -u):$(id -g) $HOME/.kube/config

Alternatively, if you are the root user, you can run:

  export KUBECONFIG=/etc/kubernetes/admin.conf

You should now deploy a pod network to the cluster.
Run "kubectl apply -f [podnetwork].yaml" with one of the options listed at:
  https://kubernetes.io/docs/concepts/cluster-administration/addons/

Then you can join any number of worker nodes by running the following on each as root:

kubeadm join 172.31.6.177:6443 --token vr5rat.seyprj6jvw4xy43m \
        --discovery-token-ca-cert-hash sha256:4c9b53eb03744b4cf21c5bdacd712024eb09030561714cc5545838482c8017b3

As above output mentioned copy the token in your notepad, we will need to join worker/slave to master node

Create new ‘.kube’ configuration directory and copy the configuration ‘admin.conf’ from ‘/etc/kubernetes’ directory.

sudo mkdir -p $HOME/.kube
sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
sudo chown $(id -u):$(id -g) $HOME/.kube/config

To check kubeadm version.

kubeadm version

To check master node status

kubectl get nodes

#6. Configure Pod Network and Verify Pod namespaces

Install the Weave network plugin to communicate master and worker nodes.

kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')"

Output:

serviceaccount/weave-net created

clusterrole.rbac.authorization.k8s.io/weave-net created

clusterrolebinding.rbac.authorization.k8s.io/weave-net created

role.rbac.authorization.k8s.io/weave-net created

rolebinding.rbac.authorization.k8s.io/weave-net created

daemonset.apps/weave-net created

Check node status

#7. Join Worker Node to the Cluster

Next Join two worker nodes to master.

sudo kubeadm join 172.31.6.177:6443 --token vr5rat.seyprj6jvw4xy43m --discovery-token-ca-cert-hash sha256:4c9b53eb03744b4cf21c5bdacd712024eb09030561714cc5545838482c8017b3

Output:

This node has joined the cluster:
* Certificate signing request was sent to apiserver and a response was received.
* The Kubelet was informed of the new secure connection details.

Run 'kubectl get nodes' on the control-plane to see this node join the cluster.

Check the All node status

sudo kubectl get nodes

Output:

Status:

NAME               STATUS   ROLES    AGE     VERSION

ip-172-31-16-180   Ready    master   3m19s   v1.20.5

ip-172-31-16-86    Ready    worker1   6m15s   v1.20.5

ip-172-31-21-34    Ready    worker2   3m23s   v1.20.5

To Verify Pod namespaces

sudo kubectl get pods --all-namespaces

Output:

NAMESPACE     NAME                                      READY   STATUS    RESTARTS   AGE

kube-system   coredns-6955765f44-7sw4r                  1/1     Running   0          6m46s

kube-system   coredns-6955765f44-nwwx5                  1/1     Running   0          6m46s

kube-system   etcd-ip-172-31-16-86                      1/1     Running   0          6m53s

kube-system   kube-apiserver-ip-172-31-16-86            1/1     Running   0          6m53s

kube-system   kube-controller-manager-ip-172-31-16-86   1/1     Running   0          6m53s

kube-system   kube-proxy-b5vht                          1/1     Running   0          4m5s

kube-system   kube-proxy-cm6r4                          1/1     Running   0          4m1s

kube-system   kube-proxy-jxr9z                          1/1     Running   0          6m45s

kube-system   kube-scheduler-ip-172-31-16-86            1/1     Running   0          6m53s

kube-system   weave-net-99tsd                           2/2     Running   0          93s

kube-system   weave-net-bwshk                           2/2     Running   0          93s

kube-system   weave-net-g8rg8                           2/2     Running   0          93s

We have covered Install Kubernetes cluster on Ubuntu.

#8. Deploy Sample Nginx microservice on Kubernetes

Lets create a deployment on master node named “nginx-deploy” using YAML.

sudo nano nginx-deploy.yaml

Deployment YAML file should like below

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx-app
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx-app
  template:
    metadata:
      labels:
        app: nginx-app
    spec:
      containers:
      - name: nginx-container
        image: nginx:latest
        ports:
        - containerPort: 80

Lets create a pod using kubectl command

kubectl apply -f nginx-deploy.yaml

Output:

deployment.apps/nginx-deployment created

Lets check Pod status

kubectl get pods

To check Pods all information

kubectl describe pods

To check pods IP address and its states

kubectl get pods -o wide

Expose the Nginx deployment using kubernetes nodeport (32001) service

cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Service
metadata:
  name: nginx-app
spec:
  selector: 
    app: nginx-app
  type: NodePort  
  ports:
    - port: 80
      targetPort: 80
      nodePort: 32001
EOF 

Now access the nginx service by using worked node IP and port 32001

To delete pod

kubectl delete pod fosstechnix-web-pod(pod name)

OR

kubectl delete -f fosstechnix-web-pod.yml

Conclusion:

In this article, We have covered How to Install Kubernetes Cluster on Ubuntu 20.04 LTS with kubeadm, Initializing master node, creating pod network,join worker/slave node to master, creating pod using YAML , checking the status of node,pod,namespace and deleting pod.

Troubleshooting:

[preflight] Running pre-flight checks
[WARNING IsDockerSystemdCheck]: detected "cgroupfs" as the Docker cgroup driver. The recommended driver is "systemd". Please follow the guide at https://kubernetes.io/docs/setup/cri/
error execution phase preflight: [preflight] Some fatal errors occurred:
[ERROR DirAvailable--etc-kubernetes-manifests]: /etc/kubernetes/manifests is not empty
[ERROR FileAvailable--etc-kubernetes-kubelet.conf]: /etc/kubernetes/kubelet.conf already exists
[ERROR Port-10250]: Port 10250 is in use
[ERROR FileAvailable--etc-kubernetes-pki-ca.crt]: /etc/kubernetes/pki/ca.crt already exists
[preflight] If you know what you are doing, you can make a check non-fatal with `--ignore-preflight-errors=...`
To see the stack trace of this error execute with --v=5 or higher

Solution:

Reset the kubeadm and join again

sudo kubeadm reset

We have covered How to Install Kubernetes Cluster on Ubuntu 20.04 LTS.

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Reference:

Kubernetes install kubeadm official page