Kubernetes architecture (control plane and nodes) - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Control Plane Components Role

Which component of the Kubernetes control plane is responsible for maintaining the desired state of the cluster by watching the cluster state and making changes?

A kube-controller-manager

B kube-apiserver

C kube-scheduler

D etcd

💡 Hint

Think about the component that manages controllers to reconcile cluster state.

The kube-controller-manager runs controllers that watch the cluster state and make changes to reach the desired state.

💻 Command Output

intermediate

Node Status Command Output

What is the output of the command kubectl get nodes when the cluster has two nodes named node1 and node2, both ready?

Kubernetes

kubectl get nodes

A

node1   Ready    master   10d
node2   Ready    worker   10d

B

NAME    STATUS   ROLES    AGE
node1   Ready    <none>   10d
node2   Ready    <none>   10d

C

NAME    STATUS    ROLES    AGE
node1   NotReady  <none>   10d
node2   Ready    <none>   10d

D

NAME    STATUS   ROLES    AGE
node1   Ready    <none>   5m
node2   Ready    <none>   5m

💡 Hint

Check the exact column headers and typical output format.

The kubectl get nodes command lists nodes with columns NAME, STATUS, ROLES, and AGE. Both nodes are ready with no roles assigned.

🔀 Workflow

advanced

Pod Scheduling Process

Put the steps of the Kubernetes pod scheduling process in the correct order.

A 1,2,3,4

B 1,3,2,4

C 2,1,3,4

D 1,2,4,3

💡 Hint

Think about the logical flow from detecting a pod to assigning it to a node.

The scheduler first detects unscheduled pods, filters nodes, ranks them, then binds the pod to the best node.

❓ Troubleshoot

advanced

Diagnosing Node Not Ready State

You notice a node in your Kubernetes cluster is in NotReady state. Which of the following is the most likely cause?

A The etcd database is full and cannot store new data.

B The pod running on the node has crashed.

C The kube-scheduler is overloaded and cannot assign pods.

D The kubelet on the node is not running or has lost connection to the control plane.

💡 Hint

Consider what controls node health reporting.

The kubelet reports node status to the control plane. If it stops or loses connection, the node shows as NotReady.

✅ Best Practice

expert

High Availability of Control Plane

Which setup ensures high availability of the Kubernetes control plane?

A Run multiple etcd instances on worker nodes only.

B Run a single kube-apiserver with multiple kube-scheduler instances on the same node.

C Run multiple kube-apiserver instances behind a load balancer with replicated etcd cluster.

D Run multiple kubelet processes on the control plane node.

💡 Hint

Think about redundancy and fault tolerance for control plane components.

High availability requires multiple API servers behind a load balancer and a replicated etcd cluster to avoid single points of failure.

Practice

1. Which component of Kubernetes is responsible for deciding what runs and where?

easy

A. Container runtime

B. Node

C. Pod

D. Control plane

Solution

1. Step 1: Understand Kubernetes architecture roles

   The control plane manages the cluster and makes decisions about scheduling and managing workloads.

2. Step 2: Identify the component that schedules workloads

   The control plane includes the scheduler which decides what runs and where.

3. Final Answer:

   Control plane -> Option D

4. Quick Check:

   Control plane = workload decision maker [OK]

Hint: Control plane manages; nodes run workloads [OK]

Common Mistakes:

• Confusing nodes with control plane
• Thinking containers decide scheduling
• Mixing pods with control plane

2. Which of the following is a correct component of the Kubernetes control plane?

easy

A. etcd

B. kube-proxy

C. kubelet

D. containerd

Solution

1. Step 1: List control plane components

   Control plane includes etcd, kube-apiserver, kube-controller-manager, and kube-scheduler.

2. Step 2: Identify which option is part of control plane

   etcd stores cluster data and is part of the control plane.

3. Final Answer:

   etcd -> Option A

4. Quick Check:

   etcd = control plane data store [OK]

Hint: etcd stores data in control plane [OK]

Common Mistakes:

• Confusing kubelet as control plane
• Thinking kube-proxy is control plane
• Mixing container runtime with control plane

3. Given a Kubernetes cluster, which component runs on each node to ensure containers are running properly?

medium

A. kubelet

B. kube-apiserver

C. kube-scheduler

D. etcd

Solution

1. Step 1: Identify node components

   Nodes run components like kubelet and kube-proxy to manage containers and networking.

2. Step 2: Determine which component manages container lifecycle on nodes

   kubelet runs on each node and ensures containers are running as expected.

3. Final Answer:

   kubelet -> Option A

4. Quick Check:

   kubelet = node container manager [OK]

Hint: kubelet runs on nodes to manage containers [OK]

Common Mistakes:

• Confusing kube-apiserver as node component
• Thinking scheduler runs on nodes
• Mixing etcd with node components

4. You notice pods are not starting on a node. Which component should you check first for errors on that node?

medium

A. kube-scheduler

B. kubelet

C. kube-apiserver

D. etcd

Solution

1. Step 1: Understand pod startup process

   Pods are started and managed on nodes by the kubelet component.

2. Step 2: Identify component to check for node pod issues

   Since pods fail to start on a node, kubelet logs and status should be checked first.

3. Final Answer:

   kubelet -> Option B

4. Quick Check:

   kubelet manages pods on nodes [OK]

Hint: Check kubelet logs for node pod issues [OK]

Common Mistakes:

• Checking scheduler instead of kubelet
• Looking at etcd for node pod errors
• Confusing apiserver with node issues

5. In a Kubernetes cluster, if the control plane node fails, which of the following is true?

hard

A. New pods can still be scheduled on nodes

B. Nodes automatically become control planes

C. Existing pods continue running but no new scheduling occurs

D. All pods immediately stop running

Solution

1. Step 1: Understand control plane failure impact

   The control plane manages scheduling and cluster state but nodes run pods independently.

2. Step 2: Analyze pod behavior when control plane is down

   Existing pods keep running on nodes, but no new pods can be scheduled without control plane.

3. Final Answer:

   Existing pods continue running but no new scheduling occurs -> Option C

4. Quick Check:

   Control plane down = no new scheduling, pods run [OK]

Hint: Control plane down stops scheduling, not running pods [OK]

Common Mistakes:

• Thinking pods stop immediately
• Assuming nodes become control planes
• Believing new pods schedule without control plane