Kubernetes Cluster Setup with kubeadm

This guide explains how to set up a Kubernetes cluster from scratch using kubeadm, containerd, and Flannel as the CNI (Container Network Interface).

---

🖥️ Prerequisites

• Multiple Linux nodes (Ubuntu recommended)
• One control plane (master) node and one or more worker nodes
• sudo privileges on all nodes
• Internet access for downloading packages

---

📦 VM Provisioning with Vagrant + VirtualBox

If you don’t want to prepare physical machines or cloud VMs manually, you can use Vagrant with VirtualBox to spin up the cluster nodes.

1. Clone this repository:

   git clone <repo-url>
   cd <repo-name>

## Inspect the included Vagrantfile and adjust CPU, memory, or network settings as needed.

## Bring up the VMs
```bash
vagrant up

Check the status

vagrant status

SSH into the nodes:

vagrant ssh controlplane
vagrant ssh node01
vagrant ssh node02

1. Install Kubernetes Components (On Every Node)

sudo apt-get update
# apt-transport-https may be a dummy package; if so, you can skip that package
sudo apt-get install -y apt-transport-https ca-certificates curl gpg
# If the directory `/etc/apt/keyrings` does not exist, it should be created before the curl command, read the note below.
# sudo mkdir -p -m 755 /etc/apt/keyrings
curl -fsSL https://pkgs.k8s.io/core:/stable:/v1.34/deb/Release.key | sudo gpg --dearmor -o /etc/apt/keyrings/kubernetes-apt-keyring.gpg
# This overwrites any existing configuration in /etc/apt/sources.list.d/kubernetes.list
echo 'deb [signed-by=/etc/apt/keyrings/kubernetes-apt-keyring.gpg] https://pkgs.k8s.io/core:/stable:/v1.34/deb/ /' | sudo tee /etc/apt/sources.list.d/kubernetes.list

# Install kubelet, kubeadm, and kubectl
sudo apt-get update
sudo apt-get install -y kubelet kubeadm kubectl
sudo apt-mark hold kubelet kubeadm kubectl
kubeadm version

---

2. Install and Configure containerd (On Every Node)

sudo apt install containerd -y
sudo mkdir -p /etc/containerd

# Generate default config and enable systemd cgroup driver
containerd config default | sed 's/SystemdCgroup = false/SystemdCgroup = true/' | sudo tee /etc/containerd/config.toml

# Verify
cat /etc/containerd/config.toml | grep -i SystemdCgroup

# Restart containerd
sudo systemctl restart containerd

---

3. Enable IPv4 Packet Forwarding (On Every Node)

# Load module now
sudo modprobe br_netfilter

# Make sure it loads on boot
echo "br_netfilter" | sudo tee /etc/modules-load.d/br_netfilter.conf

# Add missing sysctl params
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 immediately
sudo sysctl --system

Disable IPv6 on the worker (RECOMMENDED)

cat <<EOF | sudo tee /etc/sysctl.d/99-disable-ipv6.conf
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
EOF

sudo sysctl --system
sudo systemctl restart containerd
sudo systemctl restart kubelet

---

4. Configure Kubelet Cgroup Driver (On Every Node)

Check if the system is using systemd:

ps -p 1

If output is systemd, then kubeadm v1.22+ automatically defaults to the systemd cgroup driver ✅ No need to do anything about it.

---

---

Disacle Swap Memory

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

---

5. Initialize the Cluster (On Control Plane Node)

sudo kubeadm init \
  --apiserver-advertise-address <master_node_ip> \
  --pod-network-cidr "10.244.0.0/16" \
  --upload-certs

Set up kubeconfig:

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

---

6. Install Network Add-on (Calico)

Run this on the control plane node:

*before apply the manifest make sure you will set the default pod-cidr as 10.244.0.0/16. Calico will get the cidr pool automatically from kube-api-server which is running on kube-system namespace.Else you can set the cidr manually in the calico.yaml in here which lives in the calico-node DaemonSet under:

wget https://raw.githubusercontent.com/projectcalico/calico/v3.28.1/manifests/calico.yaml

- name: CALICO_IPV4POOL_CIDR
  value: "10.244.0.0/16"

• if you set the default cidr then just apply the manifest.

kubectl apply -f calico.yaml
kubectl get pods -n kube-system -w

OR Install Network Add-on (Flannel)

wget https://github.com/flannel-io/flannel/releases/latest/download/kube-flannel.yml
kubectl apply -f kube-flannel.yml

# Verify flannel pods
kubectl get po -n kube-flannel

⚠️ Make sure the CIDR block in kube-flannel.yml matches 10.244.0.0/16.

---

7. Join Worker Nodes (On Each Worker Node)

Run the join command generated by kubeadm init. You can find that command after the cluster initialization.

kubeadm join <master_node_IP>:6443 --token <token> \
  --discovery-token-ca-cert-hash <hash_token>

---

8. Label Worker Nodes (On Control Plane)

kubectl label node node01 node-role.kubernetes.io/worker=worker1
kubectl label node node02 node-role.kubernetes.io/worker=worker2

# Verify
kubectl get nodes -o wide

If you already ran kubeadm init on your control-plane node, and forget to save the 'kubeadm join' command, you can print the kubeadm join command again with:

kubeadm token create --print-join-command

---

✅ Done!

You now have a working Kubernetes cluster with containerd and Flannel networking.

When you’re done experimenting, destroy all VMs with a single command:

vagrant logout #run on each node
vagrant destroy -f