Create and manage Kubernetes clusters using kubeadm
5 minutes
5 Questions
In the context of the CKA exam, `kubeadm` is the standard tool used to bootstrap best-practice Kubernetes clusters. It automates the complex configuration of the control plane and worker nodes, abstracting the manual generation of certificates and service files while adhering to community standards…In the context of the CKA exam, `kubeadm` is the standard tool used to bootstrap best-practice Kubernetes clusters. It automates the complex configuration of the control plane and worker nodes, abstracting the manual generation of certificates and service files while adhering to community standards.
To create a cluster, you must first provision Linux hosts (virtual or physical) and install a container runtime (like containerd), along with `kubelet`, `kubeadm`, and `kubectl`. Swap memory must be disabled on all nodes. On the control plane node, you run `kubeadm init`. It is crucial to set arguments like `--pod-network-cidr` during initialization to ensure compatibility with your chosen Container Network Interface (CNI) add-on. This process initializes the etcd database and creates static pod manifests for the API server, controller manager, and scheduler.
Once the control plane is initialized, you configure `kubectl` access by copying the generated `admin.conf` to your local `.kube` directory. Subsequently, you must install a CNI plugin (such as Calico or Flannel) to enable pod networking; without this, the DNS service will not start. To add capacity, you run the `kubeadm join` command—provided at the end of the init output—on worker nodes, authenticating them via a bootstrap token and CA certificate hash.
Beyond creation, `kubeadm` is vital for cluster management. It handles version upgrades seamlessly using `kubeadm upgrade plan` and `kubeadm upgrade apply`, manages certificate renewal, and handles token lifecycle management. For the CKA, you must demonstrate proficiency in using these commands to build clusters from scratch, troubleshoot bootstrap errors, and perform rolling upgrades.
Mastering Kubeadm: Cluster Creation and Management
What is Kubeadm? Kubeadm is the official tool designed to streamline the bootstrapping of Kubernetes clusters. It creates a minimum viable, best-practice-compliant cluster. It handles the heavy lifting of setting up the Cluster Certificate Authority (CA), generating authentication certificates for all components, creating configuration files (kubeconfig), and deploying core control plane components (API Server, Controller Manager, Scheduler) as static pods.
Why is it Important? In the context of the CKA exam and real-world bare-metal or VM deployments, `kubeadm` is the standard. It bridges the gap between installing binaries and having a running cluster. Understanding it is critical for tasks involving cluster initialization, node management, and cluster version upgrades.
How it Works Kubeadm operates in phases: 1. Init: `kubeadm init` runs pre-flight checks (like ensuring Swap is off), creates the PKI (Public Key Infrastructure) in `/etc/kubernetes/pki`, generates manifests in `/etc/kubernetes/manifests`, and starts the Kubelet. 2. Join: `kubeadm join` bootstraps worker nodes by establishing a trust relationship with the control plane using a shared token and the CA certificate hash. 3. Upgrade: `kubeadm upgrade` orchestrates the version migration of the control plane components and manages the configuration updates necessary for newer Kubernetes versions.
How to Answer Questions Regarding Creating and Managing Clusters When faced with `kubeadm` questions, follow this structured approach:
Scenario A: Creating a Cluster 1. Pre-requisites: Ensure `swapoff -a` is run if required. 2. Initialization: Run `kubeadm init`. Watch for flags like `--pod-network-cidr` if the question requires a specific CNI (like Flannel or Calico). 3. Post-Install: You must configure the `.kube/config` for the user (commands provided in the `kubeadm init` output) and install a CNI plugin immediately, or the nodes will remain in `NotReady` status.
Scenario B: Upgrading a Cluster 1. Drain: Always drain the node first: `kubectl drain --ignore-daemonsets`. 2. Update Tool: Update the `kubeadm` binary via the package manager (e.g., `apt-get install kubeadm=1.xx.x-00`). 3. Plan & Apply: Run `kubeadm upgrade plan` to verify, then `kubeadm upgrade apply `. 4. Kubelet: Upgrade `kubelet` and `kubectl` packages, then reload the daemon and restart the kubelet. 5. Uncordon: Bring the node back online with `kubectl uncordon `.
Exam Tips: Answering Questions on Create and manage Kubernetes clusters using kubeadm Tip 1: Use the Output. When you run `kubeadm init`, the output literally gives you the exact commands to run next (to set up kubeconfig and to join worker nodes). Do not clear your screen; copy these immediately. Tip 2: Missing Join Command. If you are asked to join a node to an existing cluster but don't have the token, run `kubeadm token create --print-join-command` on the control plane node to generate a valid command. Tip 3: Version Precision. The CKA is strict about versions. If asked to upgrade to 1.29.1, ensure you install that exact package version. Do not just run `apt-get upgrade` as it might install a newer version than requested. Tip 4: Sudo Rights. Kubeadm commands require root privileges. Use `sudo -i` to switch to root at the start of these tasks to avoid permission errors. Tip 5: Static Pod Location. Remember that `kubeadm` relies on static pods. If the API server fails to start, check `/etc/kubernetes/manifests/` for configuration errors.