Build a Kubernetes Cluster with Kubeadm on Ubuntu 22.04

Hey everyone! 👋 Ever wanted to dive into the world of Kubernetes ? It’s the go-to platform for automating the deployment, scaling, and management of containerized applications. And trust me, once you get the hang of it, you’ll be amazed at its power and flexibility. Today, we’re going to walk through the process of setting up your own Kubernetes cluster using kubeadm on Ubuntu 22.04 . Don’t worry if you’re new to this; I’ll break it down step by step to make it as smooth as possible. We’ll cover everything from preparing your servers to deploying a sample application. Ready to get started? Let’s go!

Prerequisites: Setting the Stage

Before we dive into the nitty-gritty of Kubernetes cluster creation, let’s make sure we have everything we need. You’ll need a few things in place to ensure a successful setup. First and foremost , you’ll need access to at least two Ubuntu 22.04 servers. One will act as your control plane (the master node), and the others will be worker nodes. Think of the control plane as the brains of your operation , managing all the Kubernetes resources. The worker nodes are where your applications will actually run. Ideally, these servers should have a minimum of 2 CPU cores, 2GB of RAM, and at least 20GB of free disk space. Also, ensure that all servers can communicate with each other over the network, which is super important for your cluster to function correctly. This usually involves having a common network and allowing traffic between the nodes. Make sure to check that your firewall settings aren’t blocking any essential ports (like the Kubernetes API server port, the kubelet port, etc.) - this can save you from a lot of head-scratching later on. You should have sudo privileges on all your servers, as we’ll be making changes that require elevated permissions. A stable internet connection on each server is also a must, as we’ll be downloading and installing several packages. One often overlooked, but critical, step is to disable swap space. Kubernetes has some issues with swap enabled, so it’s a good practice to disable it. And finally, although not strictly a requirement, a basic understanding of Linux commands and networking concepts will be helpful. This includes things like how to navigate the command line, how to use ssh to connect to your servers, and how to understand basic network configurations. Don’t worry, even if you’re a beginner, I’ll provide clear instructions and explanations along the way. Now, let’s get down to the actual preparation!

Server Preparation: Getting Ready to Rumble

Now that we have all the prerequisites sorted, it’s time to prepare your Ubuntu servers for the Kubernetes installation. This involves updating packages, configuring networking, and installing some essential tools. First, start by updating your package lists and upgrading the installed packages on all your servers. This ensures that you have the latest security patches and bug fixes. You can do this by running the following commands: sudo apt update and sudo apt upgrade -y . Next up, we need to disable the swap space. This is a crucial step because Kubernetes performs better when swap is disabled. Run sudo swapoff -a to disable the swap. Then, to make the change permanent, comment out the swap entry in the /etc/fstab file. You can edit this file using a text editor like nano or vim . Open the file with sudo nano /etc/fstab and comment out the line that starts with swap . Save the file and exit. Moving on, we need to configure the networking. Ensure that your servers have a static IP address or that you have configured DHCP reservations in your network to provide consistent IP addresses. This is critical because Kubernetes components need to be able to communicate with each other using fixed IP addresses. Also, it’s a good idea to set a hostname for each server to make it easier to identify them in the cluster. You can set the hostname with the hostnamectl set-hostname command and then verify it with the hostname command. For example, on your master node, you might set the hostname to k8s-master , and on your worker nodes, you can set it to k8s-worker-1 , k8s-worker-2 , and so on. Finally, we need to install containerd , which is the container runtime that Kubernetes will use. Run the following commands to install containerd : sudo apt install containerd -y , create the configuration file with sudo mkdir -p /etc/containerd and sudo containerd config default | sudo tee /etc/containerd/config.toml , then restart containerd service with sudo systemctl restart containerd . Once you have completed these steps, your servers are ready to have Kubernetes installed. Remember to perform these preparation steps on all your servers, both the master node and the worker nodes. This will set the foundation for a smooth Kubernetes installation and configuration.

Installing Kubernetes Components: The Heart of the Matter

Alright, it’s time to install the Kubernetes components. This includes kubeadm , kubelet , and kubectl . These are the core tools you’ll need to manage your cluster. Start by adding the Kubernetes repository to your system. Run these commands to do so: sudo apt-get update , sudo apt-get install -y apt-transport-https ca-certificates curl , sudo curl -fsSLo /usr/share/keyrings/kubernetes-archive-keyring.gpg https://packages.cloud.google.com/apt/doc/apt-key.gpg , and then echo 'deb [signed-by=/usr/share/keyrings/kubernetes-archive-keyring.gpg] https://packages.cloud.google.com/apt/ kubernetes-xenial main' | sudo tee /etc/apt/sources.list.d/kubernetes.list . Then, update the package list again with sudo apt update . Now, install the kubeadm , kubelet , and kubectl packages using the command sudo apt install -y kubeadm kubelet kubectl . It’s important to note that you should not install a specific version yet, as we’ll initialize the cluster with kubeadm , which will handle the versioning. After installation, hold the kubelet package to prevent it from being automatically upgraded. Run the command sudo apt-mark hold kubelet . This ensures that kubelet doesn’t get automatically upgraded, which could potentially break your cluster if there’s a version mismatch with kubeadm . Next, initialize the Kubernetes control plane on your master node using kubeadm init . This command will set up the necessary components on the master node and provide you with the commands you’ll need to join worker nodes to the cluster. When you run kubeadm init , it’s crucial to specify the --pod-network-cidr option. This option defines the IP address range for the pods in your cluster. Choose a CIDR block that doesn’t overlap with your existing network. A common choice is 10.244.0.0/16 . The full command might look something like this: sudo kubeadm init --pod-network-cidr=10.244.0.0/16 . Make a note of the output of this command, as it will give you important information, including the kubeadm join command you’ll use to add worker nodes to the cluster. After the initialization, you’ll need to set up your kubectl configuration to connect to the cluster. Run the commands provided in the output of kubeadm init . These commands typically involve creating a .kube directory in your home directory and copying the config file. Also, after initializing the cluster, you must deploy a networking solution. Kubernetes uses a networking solution to enable communication between pods. We’ll be using Calico for this, but there are other options available. You can deploy Calico with the following command: kubectl apply -f https://raw.githubusercontent.com/projectcalico/calico/v3.26.1/manifests/calico.yaml . Finally, verify that everything is working correctly by checking the status of your nodes with the command kubectl get nodes . You should see your master node in the Ready state. Congratulations! You’ve successfully installed the core Kubernetes components and initialized your control plane.

Joining Worker Nodes: Expanding Your Horizon

Once the control plane is set up, the next step is to add worker nodes to your Kubernetes cluster. This is where your applications will actually run. Remember that kubeadm join command you got from the output of kubeadm init ? Now’s the time to use it. Copy the kubeadm join command from the master node and run it on each of your worker nodes . This command will register the worker nodes with the control plane and make them part of the cluster. Before running the kubeadm join command on the worker nodes, you must ensure that the containerd service is running and configured correctly. On the worker nodes, also check if you have followed all the server preparation steps, including disabling swap and configuring networking, which we discussed earlier. After running the kubeadm join command on a worker node, give it a few moments to register with the cluster. You can check the status of your nodes by running kubectl get nodes on the master node. The worker nodes should eventually appear in the Ready state, indicating that they are successfully joined to the cluster. If your worker nodes are not showing up as Ready , double-check the following: Is the worker node able to communicate with the master node? Are there any firewall rules blocking the required ports? Did you disable swap on the worker nodes? Did you correctly configure the container runtime ( containerd )? Are you running the correct kubeadm join command, and did you copy it from the output of kubeadm init on the master node? Once all your worker nodes are in the Ready state, your Kubernetes cluster is up and running. You can now deploy your applications to the cluster and start taking advantage of the power of Kubernetes .

Deploying a Sample Application: Putting It All to the Test

Now for the exciting part: deploying an application to your newly created Kubernetes cluster. Let’s deploy a simple