Creating a Single-Node Kubernetes Cluster with kubeadm

Creating a single-node Kubernetes cluster using kubeadm on an Ubuntu server is straightforward. Here are the detailed steps:

Step 1: Prepare the Environment

1. Update and upgrade the system:

   sudo apt update && sudo apt upgrade -y
   

2. Install required dependencies:

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

3. Disable swap (required by Kubernetes):

   bash
   1sudo swapoff -a
   2sudo sed -i '/swap/d' /etc/fstab

4. Configure kernel modules and sysctl settings:

   bash
   1sudo modprobe overlay
   2sudo modprobe br_netfilter
   3
   4cat <<EOF | sudo tee /etc/modules-load.d/k8s.conf
   5overlay
   6br_netfilter
   7EOF
   8
   9cat <<EOF | sudo tee /etc/sysctl.d/k8s.conf
   10net.bridge.bridge-nf-call-iptables  = 1
   11net.bridge.bridge-nf-call-ip6tables = 1
   12net.ipv4.ip_forward                 = 1
   13EOF
   14
   15sudo sysctl --system

Step 2: Install Docker or Container Runtime

1. Install Docker (most common runtime):

   bash
   1sudo apt install -y docker.io
   2sudo systemctl enable docker
   3sudo systemctl start docker

2. Set up the Docker daemon for Kubernetes:

   bash
   1cat <<EOF | sudo tee /etc/docker/daemon.json
   2{
   3  "exec-opts": ["native.cgroupdriver=systemd"],
   4  "log-driver": "json-file",
   5  "log-opts": {
   6    "max-size": "100m"
   7  },
   8  "storage-driver": "overlay2"
   9}
   10EOF
   11
   12sudo systemctl restart docker

Step 3: Install kubeadm, kubelet, and kubectl

1. Add the Kubernetes repository:

   bash
   1echo "deb [signed-by=/etc/apt/keyrings/kubernetes-apt-keyring.gpg] https://pkgs.k8s.io/core:/stable:/v1.28/deb/ /" | sudo tee /etc/apt/sources.list.d/kubernetes.list
   2curl -fsSL https://pkgs.k8s.io/core:/stable:/v1.28/deb/Release.key | sudo gpg --dearmor -o /etc/apt/keyrings/kubernetes-apt-keyring.gpg

2. Install Kubernetes components:

   bash
   1sudo apt update
   2sudo apt install -y kubeadm kubelet kubectl
   3sudo apt-mark hold kubeadm kubelet kubectl

Step 4: Initialize the Single-Node Cluster

1. Run the kubeadm init command:

   sudo kubeadm init --pod-network-cidr=192.168.0.0/16
   

   • Use the --pod-network-cidr flag if you're using a specific CNI (e.g., Calico).
   • This command will output a kubeadm join command—save it in case you add more nodes later.

2. Set up the kubeconfig for the user:

   bash
   1mkdir -p $HOME/.kube
   2sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
   3sudo chown $(id -u):$(id -g) $HOME/.kube/config

3. Allow the master node to schedule pods:

   kubectl taint nodes --all node-role.kubernetes.io/control-plane-
   

Step 5: Install a Pod Network Add-on

1. Install a network plugin (e.g., Calico):

kubectl apply -f https://docs.projectcalico.org/manifests/calico.yaml

Step 6: Verify the Cluster

1. Check the status of the nodes:

   kubectl get nodes
   

2. Check the status of pods in all namespaces:

   bash
   1# Check the status of pods in all namespaces
   2kubectl get pods -A