Kubeadm is a tool provided by the Kubernetes project to simplify the process of setting up a Kubernetes cluster. It automates the installation and configuration of the control plane components, making it easier to get a cluster up and running quickly.

• Cluster Bootstrapping: Simplifies the process of creating a new Kubernetes cluster.
• Control Plane Setup: Automates the setup of the Kubernetes control plane components.
• Node Joining: Provides commands to easily add new nodes to an existing cluster.
• Upgrades: Facilitates the upgrade process of Kubernetes clusters.

Before you can use Kubeadm, you need to install it on your system. The following steps outline the installation process for a Linux-based system.

• A machine with a supported Linux distribution (e.g., Ubuntu, CentOS).
• Root or sudo access to the machine.
• A network connection to download the necessary packages.

1. Update the package index and install dependencies:

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

2. Download the Google Cloud public signing key:

   sudo curl -fsSLo /usr/share/keyrings/kubernetes-archive-keyring.gpg https://packages.cloud.google.com/apt/doc/apt-key.gpg
   

3. Add the Kubernetes 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
   

4. Update the package index again and install Kubeadm, Kubelet, and Kubectl:

   sudo apt-get update
   sudo apt-get install -y kubelet kubeadm kubectl
   sudo apt-mark hold kubelet kubeadm kubectl
   

Once Kubeadm is installed, you can use it to initialize a new Kubernetes cluster.

1. Initialize the control plane node:

   sudo kubeadm init --pod-network-cidr=10.244.0.0/16
   

   • The --pod-network-cidr flag specifies the CIDR range for the pod network. This example uses the Flannel network plugin.

2. Set up the local kubeconfig:

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

3. Deploy a pod network to the cluster:

   kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml
   

4. Join worker nodes to the cluster:

   • On each worker node, run the command provided by kubeadm init to join the node to the cluster. It will look something like this:

   sudo kubeadm join <master-ip>:<master-port> --token <token> --discovery-token-ca-cert-hash sha256:<hash>
   

Kubeadm simplifies the process of upgrading a Kubernetes cluster. The following steps outline the upgrade process.

1. Upgrade the control plane node:

   sudo apt-get update
   sudo apt-get install -y kubeadm=<new-version>
   sudo kubeadm upgrade plan
   sudo kubeadm upgrade apply <new-version>
   

2. Upgrade kubelet and kubectl on the control plane node:

   sudo apt-get install -y kubelet=<new-version> kubectl=<new-version>
   sudo systemctl restart kubelet
   

3. Upgrade the worker nodes:

   • On each worker node, upgrade kubeadm:

   sudo apt-get update
   sudo apt-get install -y kubeadm=<new-version>
   sudo kubeadm upgrade node
   

   • Then, upgrade kubelet and kubectl:

   sudo apt-get install -y kubelet=<new-version> kubectl=<new-version>
   sudo systemctl restart kubelet
   

If you need to reset the cluster, you can use the following command:

• This command will remove all the components installed by Kubeadm, allowing you to start fresh.

Objective: Set up a Kubernetes cluster with one control plane node and one worker node using Kubeadm.

Steps:

1. Install Kubeadm, Kubelet, and Kubectl on both the control plane and worker nodes.
2. Initialize the control plane node using kubeadm init.
3. Set up the local kubeconfig on the control plane node.
4. Deploy a pod network (e.g., Flannel) to the cluster.
5. Join the worker node to the cluster using the kubeadm join command.
6. Verify that the cluster is up and running by checking the status of the nodes and pods.

Solution:

1. Follow the installation steps outlined in the "Installing Kubeadm" section.
2. Initialize the control plane node:

   sudo kubeadm init --pod-network-cidr=10.244.0.0/16
   

3. Set up the local kubeconfig:

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

4. Deploy the Flannel pod network:

   kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml
   

5. Join the worker node to the cluster using the command provided by kubeadm init:

   sudo kubeadm join <master-ip>:<master-port> --token <token> --discovery-token-ca-cert-hash sha256:<hash>
   

6. Verify the cluster status:

   kubectl get nodes
   kubectl get pods --all-namespaces
   

In this section, we covered the basics of Kubeadm, including its installation, cluster initialization, and management. Kubeadm simplifies the process of setting up and managing a Kubernetes cluster, making it an essential tool for Kubernetes administrators. By following the steps and exercises provided, you should now have a functional Kubernetes cluster and a solid understanding of how to use Kubeadm.