Kubernetes architecture (control plane and nodes) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the role of the Kubernetes control plane?

The control plane manages the Kubernetes cluster. It makes decisions like scheduling pods, responding to cluster events, and maintaining the desired state of the cluster.

beginner

Name the main components of the Kubernetes control plane.

The main components are: API Server, Scheduler, Controller Manager, and etcd (the key-value store).

beginner

What is a Kubernetes node?

A node is a worker machine in Kubernetes. It runs the applications and services inside containers.

intermediate

What components run on a Kubernetes node?

Each node runs kubelet (agent), container runtime (like Docker or containerd), and kube-proxy (networking).

intermediate

How does the control plane communicate with nodes?

The control plane communicates with nodes through the API Server. Nodes run kubelet which talks to the API Server to receive instructions and report status.

Which component stores the cluster state in Kubernetes?

A kube-proxy

B kubelet

C Scheduler

D etcd

etcd is the key-value store that holds the cluster's state data.

What is the main function of the kubelet on a node?

A Schedule pods to nodes

B Manage network traffic

C Run containers and report node status

D Store cluster data

kubelet runs on nodes to manage containers and report status to the control plane.

Which component is responsible for scheduling pods to nodes?

A Scheduler

B API Server

C Controller Manager

D kube-proxy

The Scheduler decides which node a pod should run on.

What does kube-proxy do on a Kubernetes node?

A Runs containers

B Manages network rules for pod communication

C Stores cluster state

D Schedules pods

kube-proxy manages network traffic and rules to enable communication between pods and services.

How does the control plane maintain the desired state of the cluster?

A By using the Controller Manager to monitor and adjust resources

B By running containers directly

C By storing data in kubelet

D By managing network traffic

The Controller Manager watches the cluster state and makes changes to keep it as desired.

Explain the roles of the Kubernetes control plane components and how they work together.

Think of the control plane as the brain of the cluster coordinating everything.

Describe what happens on a Kubernetes node and the role of its components.

Nodes are like workers that run the actual applications.

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