Kubernetes architecture (control plane and nodes) - Commands & Configuration

Introduction

Kubernetes helps run many applications on many computers easily. It does this by splitting work between a control center and worker computers called nodes. This setup keeps apps running smoothly and lets you add or fix computers without stopping everything.

When you want to manage many app copies across several computers automatically

When you need to fix or add computers without stopping your app

When you want a central place to control how apps run on many machines

When you want to keep apps running even if some computers fail

When you want to organize computers into groups for different tasks

Commands

This command shows all the worker computers (nodes) connected to the Kubernetes control plane. It helps you see which computers are ready to run apps.

Terminal

kubectl get nodes

Expected Output

NAME           STATUS   ROLES    AGE   VERSION

worker-node1   Ready    <none>   10d   v1.27.3

worker-node2   Ready    <none>   10d   v1.27.3

This command lists all running app parts (pods) in all groups (namespaces). It shows what the control plane is managing on the nodes.

Terminal

kubectl get pods -A

Expected Output

NAMESPACE     NAME                                   READY   STATUS    RESTARTS   AGE

kube-system   coredns-66bff467f8-7x9q2              1/1     Running   0          10d

kube-system   kube-proxy-worker-node1                1/1     Running   0          10d

→

-A - Show pods in all namespaces

This command shows the main addresses of the Kubernetes control plane components. It helps confirm the control center is running and reachable.

Terminal

kubectl cluster-info

Expected Output

Kubernetes control plane is running at https://192.168.1.100:6443

CoreDNS is running at https://192.168.1.100:6443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy

Key Concept

If you remember nothing else from this pattern, remember: Kubernetes splits control tasks to the control plane and runs apps on worker nodes to keep everything organized and reliable.

Common Mistakes

Trying to run app containers directly on nodes without using Kubernetes pods

This bypasses Kubernetes management, causing loss of benefits like automatic restarts and scaling

Always deploy apps as pods managed by Kubernetes through manifests or commands

Ignoring node status and assuming all nodes are ready

If nodes are NotReady, apps won't run properly and may fail silently

Use 'kubectl get nodes' regularly to check node health before deploying apps

Summary

Use 'kubectl get nodes' to see all worker computers ready to run apps.

Use 'kubectl get pods -A' to view all app parts running across the cluster.

Use 'kubectl cluster-info' to check the control plane's main addresses and status.

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