What is Kubeadm?

Kubeadm is an excellent tool to set up a working Kubernetes cluster in less time.

We can create a Kubernetes cluster without much complex configuration.

It is developed and maintained by the official Kubernetes community.

Kubeadm Setup Prerequisites

For the Kubeadm Kubernetes cluster setup, we need:

• Minimum two Ubuntu nodes [One master and one worker node]. You can have more worker nodes as per your requirement.
• The control pane [master-node] should have a minimum of 2vCPU and 2GB RAM.
• For the worker nodes, a minimum of 1vCPU and 2 GB RAM is recommended.

Kubeadm Port Prerequisites

For Control Plane:

For worker nodes:

Go to your AWS Console > EC2 instances > Launch an instance.

Let's start by creating two EC2 [Ubuntu] instances, one for control-plane and the other as a worker node.

For each, we will use t2.medium, as the instances should satisfy the resource requirements.

Let's launch the instances.

Let's satisfy the port requirements for control-plane:

Go to your control-plane instance, look for the security tab and click on security groups.

Then click on Edit Inbound rules:

Here, add the ports required for the control pane:

Then click Save rules.

Similarly, add the required ports for the worker nodes as well.

After editing the inbound rules, we are good to go with setting up our cluster.

Steps to setup Kubernetes cluster using kubeadm

1. Install container runtime on all nodes- We will be using cri-o.
2. Install Kubeadm, Kubelet, and Kubectl on all nodes.
3. Initiate Kubeadm control plane configuration on the master node.
4. Save the node join command with the token.
5. Join the worker node to the master node [control plane] using the join command.

Let's start the setup, and execute the below commands on all the nodes

Enable iptables Bridged Traffic on all the Nodes

cat <<EOF | sudo tee /etc/modules-load.d/k8s.conf
overlay
br_netfilter
EOF

sudo modprobe overlay
sudo modprobe br_netfilter

# sysctl params required by setup, params persist across reboots
cat <<EOF | sudo tee /etc/sysctl.d/k8s.conf
net.bridge.bridge-nf-call-iptables  = 1
net.bridge.bridge-nf-call-ip6tables = 1
net.ipv4.ip_forward                 = 1
EOF

# Apply sysctl params without reboot
sudo sysctl --system

Disable swap on all the Nodes

sudo swapoff -a (crontab -l 2>/dev/null; echo "@reboot /sbin/swapoff -a") | crontab - || true

Install CRI-O Runtime On All The Nodes

cat <<EOF | sudo tee /etc/modules-load.d/crio.conf 
overlay 
br_netfilter
EOF 

# Set up required sysctl params, these persist across reboots.
cat <<EOF | sudo tee /etc/sysctl.d/99-kubernetes-cri.conf 
net.bridge.bridge-nf-call-iptables = 1 
net.ipv4.ip_forward = 1 
net.bridge.bridge-nf-call-ip6tables = 1 
EOF

Execute the following commands to enable overlayFS & VxLan pod communication.

sudo modprobe overlay 
sudo modprobe br_netfilter

Set up required sysctl params, these persist across reboots.

cat <<EOF | sudo tee /etc/sysctl.d/99-kubernetes-cri.conf
net.bridge.bridge-nf-call-iptables  = 1
net.ipv4.ip_forward                 = 1
net.bridge.bridge-nf-call-ip6tables = 1
EOF

Reload the parameters.

sudo sysctl --system

Enable cri-o repositories for version 1.23

OS="xUbuntu_22.04"

VERSION="1.23"

cat <<EOF | sudo tee /etc/apt/sources.list.d/devel:kubic:libcontainers:stable.list
deb https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$OS/ /
EOF
cat <<EOF | sudo tee /etc/apt/sources.list.d/devel:kubic:libcontainers:stable:cri-o:$VERSION.list
deb http://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable:/cri-o:/$VERSION/$OS/ /
EOF

Add the gpg keys.

curl -L 
https://download.opensuse.org/repositories/devel:kubic:libcontainers:stable:cri-o:$VERSION/$OS/Release.key | sudo apt-key --keyring /etc/apt/trusted.gpg.d/libcontainers.gpg add -
curl -L 
https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$OS/Release.key | sudo apt-key --keyring /etc/apt/trusted.gpg.d/libcontainers.gpg add -

Update and install crio and crio-tools.

sudo apt-get update 
sudo apt-get install cri-o cri-o-runc cri-tools -y

Reload the systemd configurations and enable cri-o.

sudo systemctl daemon-reload
sudo systemctl enable crio --now

Install Kubeadm & Kubelet & Kubectl on all Nodes

sudo apt-get update
sudo apt-get install -y apt-transport-https ca-certificates curl

Download the signing key

sudo curl -fsSL https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo gpg --dearmor -o /etc/apt/keyrings/kubernetes-archive-keyring.gpg

Add the GPG key and apt repository.

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 apt repo

sudo apt-get update -y
sudo apt update
apt-cache madison kubeadm | tac

curl -sSL https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo gpg --dearmor -o /usr/share/keyrings/kubernetes.gpg

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

sudo apt update

Install kubelet, kubeadm, kubectl

sudo apt-get install -y kubelet=1.27.3-00 kubectl=1.27.3-00 kubeadm=1.27.3-00

Now, hold the versions for kubelet, kubeadm, kubectl

sudo apt-mark hold kubelet kubeadm kubectl

Add the node IP to KUBELET_EXTRA_ARGS.

sudo apt-get install -y jq
local_ip="$(ip --json a s | jq -r '.[] | if .ifname == "eth1" then .addr_info[] | if .family == "inet" then .local else empty end else empty end')"
cat > /etc/default/kubelet << EOF
KUBELET_EXTRA_ARGS=--node-ip=$local_ip
EOF

Initialize Kubeadm On Master Node To Setup Control Plane

Master Node With Public IP: If you are setting up a Kubeadm cluster on Cloud platforms and you need master Api server access over the Public IP of the master node server.

You can also use Private IP, but let's proceed with Public IP as we using AWS.

Set the following environment variables. The IPADDR variable will be automatically set to the server’s public IP using ifconfig.me curl call. You can also replace it with a public IP address.

IPADDR=$(curl ifconfig.me && echo "")
NODENAME=$(hostname -s)
POD_CIDR="192.168.0.0/16"

sudo kubeadm init --control-plane-endpoint=$IPADDR  --apiserver-cert-extra-sans=$IPADDR  --pod-network-cidr=$POD_CIDR --node-name $NODENAME --ignore-preflight-errors Swap

On a successful kubeadm initialization, you should get an output with kubeconfig file location and the join command with the token as shown below. Copy that and save it to the file. we will need it for joining the worker node to the master.

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

Now, verify the kubeconfig by executing the following kubectl command to list all the pods in the kube-system namespace.

kubectl get po -n kube-system

kubectl cluster-info

Join Worker Nodes To Kubernetes Master Node

We have set up cri-o, kubelet, and kubeadm utilities on the worker nodes as well.

Now, let’s join the worker node to the master node using the Kubeadm join command you have got in the output while setting up the master node.

If you missed copying the join command, execute the following command in the master node to recreate the token with the join command.

kubeadm token create --print-join-command

The command will look something like this,

sudo kubeadm join 10.128.0.37:6443
 --token j4eice.33vgvgyf5cxw4u8i \
 --discovery-token-ca-cert-hash 
sha256:37f94469b58bcc8f26a4aa44441fb17196a585b37288f85e22475b00c36f1c61
# do not use this command, this is just for example

Execute this command on the worker node, if you get

"This node has joined the cluster"

The node was added to cluster 🎉

Now execute the kubectl command from the master node to check if the node is added to the master.

kubectl get nodes

If you get the nodes, Congratulations 🎉

You can see, in our output, the ROLE is <none> for the worker nodes. You can add a label to the worker node using the following command. Replace worker-node01 with the hostname of the worker node you want to label.

kubectl label node worker-node01 node-role.kubernetes.io/worker=worker
#please replace hostname

You can further add more nodes with the same join command.

Thank you!