The kubeadm tool helps you bootstrap a minimum viable Kubernetes cluster that conforms to best practices.

The kubeadm tool is good if you need:

• A simple way for you to try out Kubernetes, possibly for the first time.
• A way for existing users to automate setting up a cluster and test their application.
• A building block in other ecosystem and/or installer tools with a larger scope.

Before you begin

To follow this guide, you need:

• One or more machines running a deb/rpm-compatible Linux OS; for example: Ubuntu or CentOS.
• 2 GiB or more of RAM per machine–any less leaves little room for your apps.
• At least 2 CPUs on the machine that you use as a control-plane node.
• Full network connectivity among all machines in the cluster. You can use either a public or a private network.

Check required ports

Control-plane node(s)

Worker node(s)

Installing runtime

By default, Kubernetes uses the Container Runtime Interface (CRI) to interface with your chosen container runtime.

If you don’t specify a runtime, kubeadm automatically tries to detect an installed container runtime by scanning through a list of well known Unix domain sockets.

If both Docker and containerd are detected, Docker takes precedence. This is needed because Docker 18.09 ships with containerd and both are detectable even if you only installed Docker. If any other two or more runtimes are detected, kubeadm exits with an error.

Installing kubeadm, kubelet and kubectl 

• 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.

Infrastructure

Lets Create 3 VirtualMachines(VMs) (1 Master Node and 2 Worker node). There must be network connectivity among these VMs

Installation on Ubuntu (Both on Master and Worker Nodes)

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

apt install -qq -y kubeadm=1.27.2-00 kubelet=1.27.2-00 kubectl=1.27.2-00

sudo apt-mark hold kubelet kubeadm kubectl

Create Master Server

On master machine run the below command

1. kubeadm init –apiserver-advertise-address=<<Master ServerIP>> –pod-network-cidr=192.168.0.0/16

2. mkdir -p $HOME/.kube
3. sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
4. sudo chown $(id -u):$(id -g) $HOME/.kube/config
5. Run the join command on workernodes to connect these on kubernetes cluster.

Install Calico (run it only on master node)

kubectl create -f https://docs.projectcalico.org/v3.18/manifests/calico.yaml

kubectl get nodes

Wait for above command and run again it may take a minute or so to get all the nodes in ready state.

Installation on RHEL/CentOS (Both on Master and Worker Nodes)

In case if you are using CentOS/RHEL

cat <<EOF | sudo tee /etc/yum.repos.d/kubernetes.repo[kubernetes]name=Kubernetesbaseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-\$basearchenabled=1gpgcheck=1repo_gpgcheck=1gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg \ https://packages.cloud.google.com/yum/doc/rpm-package-key.gpgexclude=kubelet kubeadm kubectlEOF # Set SELinux in permissive mode (effectively disabling it)sudo setenforce 0sudo sed -i ‘s/^SELINUX=enforcing$/SELINUX=permissive/’ /etc/selinux/config sudo yum install -y kubelet kubeadm kubectl –disableexcludes=kubernetes sudo systemctl enable –now kubelet