Troubleshooting cluster components is a critical domain in the Certified Kubernetes Administrator (CKA) curriculum, focusing on diagnosing failures within the Control Plane and Worker Nodes. The workflow involves isolating whether the issue lies with the cluster services (systemd) or the Kubernetes…Troubleshooting cluster components is a critical domain in the Certified Kubernetes Administrator (CKA) curriculum, focusing on diagnosing failures within the Control Plane and Worker Nodes. The workflow involves isolating whether the issue lies with the cluster services (systemd) or the Kubernetes components (Pods/Containers).
**1. Control Plane Failure:**
Most control plane components (API Server, Scheduler, Controller Manager) run as Static Pods. If the API server is unreachable, `kubectl` will not work. You must SSH into the master node and:
- **Check the Kubelet:** The kubelet manages static pods. Use `systemctl status kubelet` and `journalctl -u kubelet` to ensure it is active.
- **Verify Manifests:** Check `/etc/kubernetes/manifests` for YAML syntax errors or misconfigurations (e.g., incorrect command arguments or volume mounts).
- **Container Logs:** Since the API is down, use `crictl ps` and `crictl logs <container-id>` or inspect `/var/log/pods` directly to identify why a component crashed.
- **PKI/Certificates:** Ensure certificates in `/etc/kubernetes/pki` are valid and not expired.
**2. Worker Node Failure:**
Nodes often report a `NotReady` status.
- **Kubelet Status:** This is the primary agent. If it is stopped, the node cannot report to the control plane. Check its configuration file (usually `/var/lib/kubelet/config.yaml`) and restart the service.
- **Container Runtime:** Ensure the runtime (containerd/CRI-O) is running via `systemctl status containerd`.
- **CNI/Networking:** If pods are pending or nodes are NotReady, check if the CNI plugin is correctly installed and initialized.
**3. ETCD:**
A failed ETCD cluster halts all cluster operations. Troubleshoot by checking `journalctl` logs for the etcd service or static pod, verifying data directory permissions, and ensuring leader election is successful.
Success requires mastery of `systemctl`, `journalctl`, `crictl`, and locating standard config paths.
Troubleshooting Cluster Components
Why is it Important? Kubernetes is a complex distributed system. While applications fail often, the underlying infrastructure components (the Control Plane and Worker Node services) can also fail due to misconfiguration, certificate expiration, or resource exhaustion. Being able to diagnose and fix the cluster components is the hallmark of a competent administrator. Furthermore, Troubleshooting carries a significant weight (approx. 30%) in the CKA exam, meaning you cannot pass without mastering this section.
What is it? Troubleshooting cluster components refers to the process of identifying and resolving issues with the core binaries and services that make Kubernetes work. This includes the Control Plane (kube-apiserver, etcd, kube-scheduler, kube-controller-manager) and the Worker Nodes (kubelet, kube-proxy, container runtime like containerd). Unlike application troubleshooting, this requires direct access to the node's operating system and configuration files.
How it Works Cluster components generally run in one of two ways: as Native System Services (managed by systemd) or as Static Pods (managed by the Kubelet).
1. Worker Node Failures: Usually involve the kubelet. Since the kubelet manages pods, if it crashes, the node becomes 'NotReady'. You diagnose this by SSH-ing into the node and checking the system service status (systemctl status kubelet) and logs (journalctl -u kubelet). 2. Control Plane Failures: Often involve Static Pods located in /etc/kubernetes/manifests/. If the API server is down, kubectl commands will fail. You must access the master node, check if the container runtime is active, and inspect the manifest files for syntax errors or typos.
How to Answer Questions Regarding Troubleshoot Cluster Components In the exam, you will likely face a scenario where a node is 'NotReady' or the cluster is unresponsive. Step 1: Identify the Scope. Run kubectl get nodes. Is it one node or all of them? If kubectl fails entirely, the issue is on the Control Plane node. Step 2: Access the Node. SSH into the problematic node (e.g., ssh node01). Step 3: Check the Kubelet. It is the most common point of failure. Run systemctl status kubelet. Step 4: Check Logs. If the service is failed, run journalctl -u kubelet | tail -n 20 to see the error (e.g., 'certificate not found', 'config.yaml not found'). Step 5: Fix and Restart. Correct the configuration file, fix the path, or start the stopped service. Always run systemctl daemon-reload and systemctl restart kubelet after config changes.
Exam Tips: Answering Questions on Troubleshoot cluster components 1. Know the Paths: Memorize that Static Pod manifests live in /etc/kubernetes/manifests/ and Kubelet config is usually in /var/lib/kubelet/config.yaml. 2. Watch for Typos: A very common exam task involves a Static Pod (like the Scheduler) failing because someone typed the image name wrong or misspelled a command in the YAML file. If a component is crash-looping, check the YAML first. 3. Check Certificates: If logs say 'x509: certificate signed by unknown authority' or 'no such file', check that the certificate file paths in the Kubelet config or API server manifest actually point to valid files on the disk. 4. Don't Panic on API Failure: If the API server is down, kubectl won't work. You must use crictl ps or docker ps on the master node to see if the API server container is running. 5. Verify Status: After applying a fix, always verify the node status changed to 'Ready' using kubectl get nodes before moving to the next question.