Node components (kubelet, kube-proxy, container runtime) in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Role of kubelet in a Kubernetes node

Which of the following best describes the primary role of the kubelet on a Kubernetes node?

A It manages network traffic routing between pods and services.

B It runs and manages containers on the node according to PodSpecs.

C It stores cluster state and configuration data.

D It schedules pods to nodes based on resource availability.

💡 Hint

Think about which component talks directly to the container runtime to start containers.

The kubelet is the agent on each node that ensures containers described in PodSpecs are running and healthy. It communicates with the container runtime to start and stop containers.

💻 Command Output

intermediate

Output of checking kube-proxy status

What is the expected output when running kubectl get pods -n kube-system -l k8s-app=kube-proxy on a healthy cluster?

A A list of kube-proxy pods with status 'Running' on each node.

B A list of kubelet pods with status 'Pending'.

C Error: the server doesn't have a resource type 'pods'.

D No resources found in kube-system namespace.

💡 Hint

kube-proxy runs as a DaemonSet in the kube-system namespace.

The command lists pods labeled with k8s-app=kube-proxy in the kube-system namespace. On a healthy cluster, kube-proxy pods run on each node and show status 'Running'.

❓ Configuration

advanced

Configuring container runtime for Kubernetes node

Which configuration file is commonly used to specify the container runtime endpoint for the kubelet on a Kubernetes node?

A /etc/systemd/system/kubelet.service.d/10-kubeadm.conf

B /etc/containerd/config.toml

C /var/lib/kubelet/kubeadm-flags.env

D /etc/kubernetes/kubelet.conf

💡 Hint

kubeadm sets the --container-runtime-endpoint flag in an env file loaded by the kubelet systemd service.

The file /var/lib/kubelet/kubeadm-flags.env contains KUBELET_EXTRA_ARGS with the --container-runtime-endpoint flag, which is loaded by the kubelet systemd service.

❓ Troubleshoot

advanced

Troubleshooting kube-proxy network issues

If pods on different nodes cannot communicate but pods on the same node can, which kube-proxy mode is most likely causing the problem?

A none of the above; kube-proxy does not affect pod communication

B userspace mode with firewall blocking ports

C iptables mode with incorrect IP forwarding settings

D ipvs mode with missing kernel modules

💡 Hint

Direct pod-to-pod communication across nodes is handled by the CNI plugin, not kube-proxy.

kube-proxy manages access to Services (ClusterIP, NodePort, LoadBalancer). Direct pod-to-pod IP communication between nodes is handled by the CNI network plugin (e.g., Calico, Flannel). This symptom typically indicates a CNI issue, such as disabled IP forwarding (net.ipv4.ip_forward=0).

✅ Best Practice

expert

Choosing container runtime for Kubernetes nodes

Which container runtime is recommended by Kubernetes for best compatibility and support as of 2024?

A rkt

B Docker Engine

C CRI-O

D containerd

💡 Hint

Consider the runtime that Kubernetes directly supports and maintains integration with.

Kubernetes recommends containerd as the default container runtime because it is lightweight, stable, and directly supported by the Kubernetes community.