kubeadm init

The kubeadm init command is used to bootstrap the first control plane node in a Kubernetes cluster. Here's how you can initialize a control plane node step-by-step:

---

1. Prerequisites

Ensure the Following:

• Operating System: Use a supported Linux distribution (e.g., Ubuntu, CentOS, etc.).
• Container Runtime: Install a supported container runtime like containerd or CRI-O.
• kubeadm, kubelet, kubectl Installed: Install these tools using your package manager.

  apt update && apt install -y kubeadm kubelet kubectl
  

  Or on CentOS:

  yum install -y kubeadm kubelet kubectl
  

• Swap Disabled:

  swapoff -a
  sed -i '/swap/d' /etc/fstab
  

• Firewall Ports Open: Allow necessary Kubernetes ports such as 6443, 2379-2380, 10250, 10259, 10257. For example:

  sudo ufw allow 6443/tcp
  sudo ufw allow 2379:2380/tcp
  sudo ufw allow 10250:10259/tcp
  

---

2. Run kubeadm init to Bootstrap the First Control Plane

Basic Command

Run the following command on the first control plane node:

sudo kubeadm init --pod-network-cidr=<CIDR> --control-plane-endpoint=<endpoint>

• Options:
  • --pod-network-cidr=<CIDR>: The CIDR range for the pod network (e.g., 192.168.0.0/16 for Calico).
  • --control-plane-endpoint=<endpoint>: A stable hostname or IP address for your control plane (e.g., a load balancer). If not available, use the current node's IP.

Example:

sudo kubeadm init --pod-network-cidr=192.168.0.0/16 --control-plane-endpoint=192.168.1.10:6443

---

Advanced Configuration with kubeadm-config.yaml

If you need more control, use a configuration file:

1. Create a file kubeadm-config.yaml:

   apiVersion: kubeadm.k8s.io/v1beta3
   kind: ClusterConfiguration
   kubernetesVersion: "v1.28.0"
   controlPlaneEndpoint: "192.168.1.10:6443"  # Use load balancer IP if available
   networking:
     podSubnet: "192.168.0.0/16"  # For Calico or other CNI
   

2. Initialize the cluster using:

   sudo kubeadm init --config kubeadm-config.yaml
   

---

3. Post-Initialization Steps

After kubeadm init completes, it outputs instructions for further setup:

Set up kubeconfig:

To use kubectl as a non-root user:

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

Deploy a Pod Network Add-on:

Install a CNI (Container Network Interface) plugin for pod networking. For example:

• Calico:

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

• Weave Net:

  kubectl apply -f https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')
  

---

4. Join Additional Control Plane Nodes

To add more control plane nodes, retrieve the kubeadm join command:

kubeadm token create --print-join-command

This will look like:

kubeadm join <control-plane-endpoint>:6443 --token <token> \
    --discovery-token-ca-cert-hash sha256:<hash> \
    --control-plane

Run this on the additional control plane nodes.

---

5. Verify the Control Plane

Check the status of the control plane:

kubectl get nodes

Ensure the node is in a Ready state.

---

Let me know if you encounter specific issues during this process, and I can assist further!