Troubleshooting Kubernetes clusters and nodes is a pivotal competency for the CKA exam, focusing on diagnosing why nodes are 'NotReady' or why the control plane is unresponsive. The process begins with high-level observation using 'kubectl get nodes' to identify the problem scope. If a node is unhe…Troubleshooting Kubernetes clusters and nodes is a pivotal competency for the CKA exam, focusing on diagnosing why nodes are 'NotReady' or why the control plane is unresponsive. The process begins with high-level observation using 'kubectl get nodes' to identify the problem scope. If a node is unhealthy, 'kubectl describe node <node-name>' is the first step to inspect the 'Conditions' section (checking for MemoryPressure, DiskPressure, or PIDPressure) and the 'Events' stream for recent errors.
At the node level, the Kubelet is the most critical component. Since it runs as a system daemon, troubleshooting requires SSH access to the node. You must verify the service status using 'systemctl status kubelet' and analyze logs via 'journalctl -u kubelet'. Common Kubelet failure points include misconfigured CNI plugins, expired certificates in '/var/lib/kubelet/pki', or swap memory being enabled (which must be disabled). If the Kubelet is running but containers fail, check the Container Runtime (e.g., containerd) status and logs.
For Control Plane issues where the API server is unreachable, 'kubectl' commands will fail. You must access the master node directly and inspect static pod manifests in '/etc/kubernetes/manifests/'. Since control plane components run as containers, use 'crictl ps' and 'crictl logs' to diagnose the API Server, Scheduler, or Etcd. Additionally, verify certificate validity using 'kubeadm certs check-expiration'.
Effective troubleshooting follows a layered approach: validate the Node status, inspect the Kubelet and Runtime services on the host, verify network/CNI configurations, and ensure certificate validity across the cluster.
Troubleshooting Clusters and Nodes
Why is it Important? Troubleshooting is arguably the most critical skill for a Certified Kubernetes Administrator. In real-world scenarios, clusters fail due to network partitions, misconfigurations, or service crashes. The ability to diagnose and repair the cluster infrastructure ensures high availability and reliability. Furthermore, the Troubleshooting domain accounts for approximately 30% of the CKA exam score, making it essential to master for passing.
What is it? Troubleshooting clusters and nodes involves diagnosing issues at the infrastructure level rather than the application level. This includes identifying why a node is marked as NotReady, why the control plane components (like the Scheduler or Controller Manager) are unresponsive, or why the Kubelet service fails to start on a worker node. It often requires working outside of Kubernetes objects, interacting directly with the host operating system, system services (systemd), and container runtimes.
How it Works The troubleshooting workflow generally follows a hierarchical approach: 1. Identify the Broken Node: Use kubectl get nodes to see which node is NotReady. 2. Access the Node: SSH into the problematic node (e.g., ssh node01). 3. Check System Services: Verify if the Kubelet and Container Runtime (like containerd) are running using systemctl status kubelet. 4. Analyze Logs: If a service is failed, check logs using journalctl -u kubelet -f or /var/log/pods. 5. Inspect Configurations: Check the Kubelet config file usually located at /var/lib/kubelet/config.yaml or the systemd unit file. 6. Verify Certificates: Ensure client and server certificates are valid and not expired.
How to Answer Questions regarding Troubleshoot clusters and nodes in an exam? When faced with a troubleshooting question, follow this algorithm: 1. Read the Scenario: Determine if the issue is on the Control Plane (master) or a Worker Node. 2. Describe the Node: Run kubectl describe node <node-name> to look for events (e.g., DiskPressure, PIDPressure, or Kubelet stopped posting status). 3. SSH and Escalate: Log into the node. Immediately check if the Kubelet is active: systemctl status kubelet. 4. Fix the Root Cause: - If the binary path is wrong in the service file, edit it. - If the CA certificate is mismatching, correct the path in the config. - If the swap is on, turn it off (swapoff -a). 5. Restart Services: After any configuration change, run systemctl daemon-reload and systemctl restart kubelet. 6. Verify: Exit the node and ensure it returns to a Ready state.
Exam Tips: Answering Questions on Troubleshoot clusters and nodes 1. Master systemctl and journalctl: You must be comfortable checking service status and reading system logs without hesitation. Memorize journalctl -u kubelet | tail -n 20. 2. Check Static Pod Paths: If control plane components (etcd, api-server) are down, check the manifest directory (usually /etc/kubernetes/manifests). A simple typo in a YAML file here will crash the cluster. 3. Don't Panic over 'NotReady': It is almost always the Kubelet or the Container Runtime (CRI). Check if the CRI endpoint in the kubelet config matches the actual sock file of the container runtime. 4. Certificate paths: A common exam task involves a broken kubelet due to a wrong certificate path in /var/lib/kubelet/config.yaml. Compare the paths in the config file with the actual files in /etc/kubernetes/pki/. 5. Sudoless commands: Remember you are usually root on the nodes after SSH, but if not, use sudo -i immediately to save typing sudo repeatedly.