Kubeadm is a tool built to provide best-practice “fast paths” for creating Kubernetes clusters. It performs the actions necessary to get a minimum viable, secure cluster up and running in a user friendly way.

Kubernetes is an open-source container-orchestration system for automating computer application deployment, scaling, and management.

Before starting, ensure your software is up to date

sudo apt apdate
sudo apt upgrade

# Install

Install the following packages on all of your machines:

kubeadm: the command to bootstrap the cluster.
kubelet: the component that runs on all of the machines in your cluster and does things like starting PODs and containers.
kubectl: the command line util to talk to your cluster.

sudo apt-get update && sudo apt-get install -y apt-transport-https curl
curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add -
cat <<EOF | sudo tee /etc/apt/sources.list.d/kubernetes.list
deb https://apt.kubernetes.io/ kubernetes-xenial main
EOF
sudo apt-get update
sudo apt-get install -y kubelet kubeadm kubectl
sudo apt-mark hold kubelet kubeadm kubectl

Confirm installed versions

kubectl version --client

kubeadm version

Output:

vagrant@ub-kubeadm:~$ kubectl version --client
Client Version: version.Info{Major:"1", Minor:"22", GitVersion:"v1.22.0", GitCommit:"c2b5237ccd9c0f1d600d3072634ca66cefdf272f", GitTreeState:"clean", BuildDate:"2021-08-04T18:03:20Z", GoVersion:"go1.16.6", Compiler:"gc", Platform:"linux/amd64"}

vagrant@ub-kubeadm:~$ kubeadm version
kubeadm version: &version.Info{Major:"1", Minor:"22", GitVersion:"v1.22.0", GitCommit:"c2b5237ccd9c0f1d600d3072634ca66cefdf272f", GitTreeState:"clean", BuildDate:"2021-08-04T18:02:08Z", GoVersion:"go1.16.6", Compiler:"gc", Platform:"linux/amd64"}

Turn off swap.

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

Configure sysctl.

sudo modprobe overlay
sudo modprobe br_netfilter

sudo tee /etc/sysctl.d/kubernetes.conf<<EOF
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1
net.ipv4.ip_forward = 1
EOF

sudo sysctl --system

# Install Containerd Container runtime

sudo apt-get install -y containerd

Configure containerd and start service

sudo mkdir -p /etc/containerd
sudo containerd config default > /etc/containerd/config.toml

Enable the service to start on boot and start

sudo systemctl enable --now containerd

# check status
sudo systemctl status containerd

Service should be running

containerd.service - containerd container runtime
     Loaded: loaded (/lib/systemd/system/containerd.service; enabled; vendor preset: enabled)
     Active: active (running) since Wed 2021-08-04 20:27:51 UTC; 7min ago
       Docs: https://containerd.io
   Main PID: 8159 (containerd)
      Tasks: 12
     Memory: 23.3M
     CGroup: /system.slice/containerd.service
             &#x2514;&#x2500;8159 /usr/bin/containerd

Aug 04 20:27:51 ub-kubeadm containerd[8159]: time="2021-08-04T20:27:51.784407330Z" level=info msg="loading plugin \"io.containerd.grpc>
Aug 04 20:27:51 ub-kubeadm containerd[8159]: time="2021-08-04T20:27:51.785605392Z" level=info msg=serving... address=/run/containerd/c>
Aug 04 20:27:51 ub-kubeadm containerd[8159]: time="2021-08-04T20:27:51.785639559Z" level=info msg=serving... address=/run/containerd/c>
Aug 04 20:27:51 ub-kubeadm containerd[8159]: time="2021-08-04T20:27:51.787585658Z" level=info msg="containerd successfully booted in 0>
Aug 04 20:27:51 ub-kubeadm containerd[8159]: time="2021-08-04T20:27:51.801146245Z" level=info msg="Start subscribing containerd event"
Aug 04 20:27:51 ub-kubeadm containerd[8159]: time="2021-08-04T20:27:51.804843058Z" level=info msg="Start recovering state"
Aug 04 20:27:51 ub-kubeadm containerd[8159]: time="2021-08-04T20:27:51.805094249Z" level=info msg="Start event monitor"
Aug 04 20:27:51 ub-kubeadm containerd[8159]: time="2021-08-04T20:27:51.805193238Z" level=info msg="Start snapshots syncer"
Aug 04 20:27:51 ub-kubeadm containerd[8159]: time="2021-08-04T20:27:51.805282655Z" level=info msg="Start cni network conf syncer"
Aug 04 20:27:51 ub-kubeadm containerd[8159]: time="2021-08-04T20:27:51.805369362Z" level=info msg="Start streaming server"

# Initialize master node

Enable and start kubelet service.

sudo systemctl enable --now kubelet

Pull Required container images:

sudo kubeadm config images pull

Set cluster endpoint DNS name or add record to /etc/hosts file.

192.168.20.7 k8s.citizix.local

Create cluster:

sudo kubeadm init \
  --pod-network-cidr=192.168.0.0/16 \
  --control-plane-endpoint=k8s.citizix.local

When that is done, the k8s should be up and running. Obtain the kubeconfig admin file from this path /etc/kubernetes/admin.conf

mkdir ~/.kube
sudo cp /etc/kubernetes/admin.conf ~/.kube/admin.conf
sudo chown ${USER}.${GROUP} ~/.kube/admin.conf
chmod 400 ~/.kube/admin.conf

Check cluster status:

kubectl cluster-info

Confirm master node is ready:

kubectl get nodes -o wide

Additional Master nodes can be added using the command in installation output:

kubeadm join k8s-cluster.computingforgeeks.com:6443 --token sr4l2l.2kvot0pfalh5o4ik \
    --discovery-token-ca-cert-hash sha256:c692fb047e15883b575bd6710779dc2c5af8073f7cab460abd181fd3ddb29a18 \
    --control-plane

# Add worker nodes

With the control plane ready you can add worker nodes to the cluster for running scheduled workloads.

If endpoint address is not in DNS, add record to /etc/hosts.

$ sudo vim /etc/hosts
192.168.20.7 k8s.citizix.local

The join command that was given is used to add a worker node to the cluster.

kubeadm join k8s-cluster.computingforgeeks.com:6443 \
  --token sr4l2l.2kvot0pfalh5o4ik \
  --discovery-token-ca-cert-hash sha256:c692fb047e15883b575bd6710779dc2c5af8073f7cab460abd181fd3ddb29a18

Run below command on the control-plane to see if the node joined the cluster.

kubectl get nodes

Deploy application on cluster