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Cluster architecture

Learn the architecture of control plane and nodes.

Cluster architecture

A Kubernetes cluster consists of two kinds of machines:

  • Control plane: the brain of the cluster. The API server, scheduler, controllers and the etcd database run here.
  • Worker nodes: the machines where application pods actually run.

You and all the components talk to the cluster only through the API server.

$ kubectl get nodes
NAME            STATUS   ROLES           AGE   VERSION
control-plane   Ready    control-plane   12d   v1.31.2
worker-1        Ready    <none>          12d   v1.31.2
worker-2        Ready    <none>          12d   v1.31.2

Where is a pod running?

The scheduler picks a suitable node for each pod. -o wide shows which node a pod runs on and with which IP:

$ kubectl get pods -o wide
NAME                  READY   STATUS    IP           NODE
web-7c5b9f6d8-abcde   1/1     Running   10.244.1.5   worker-1
web-7c5b9f6d8-fghij   1/1     Running   10.244.2.7   worker-2

In managed services (EKS, GKE, AKS), the provider runs the control plane; you only see the worker nodes.

Practice Look at the cluster

Write two commands: list the nodes in wide format (-o wide); then list the pods together with the nodes they run on.

Starter code

terminal
# buraya yaz

Sample solution

terminal
kubectl get nodes -o wide
kubectl get pods -o wide

Expected output

NAME            STATUS   ROLES           VERSION   INTERNAL-IP
control-plane   Ready    control-plane   v1.31.2   192.168.49.2
worker-1        Ready    <none>          v1.31.2   192.168.49.3
NAME                  READY   STATUS    IP           NODE
web-7c5b9f6d8-abcde   1/1     Running   10.244.1.5   worker-1

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Which component of the cluster do kubectl commands go to?

  • Directly to etcd
  • To the worker nodes
  • To the Docker daemon
  • kube-apiserver Correct answer

Explanation: The API server authenticates, validates the request and writes to etcd.

2 List the machines in the cluster.

Question 
kubectl get ____
Answer 
kubectl get nodes

Explanation: Each machine is a node object.

3 Match.

Term Meaning
control plane The cluster's brain
worker node Runs pods
kube-apiserver Single entry point
-o wide Node and IP columns

All lessons in Intermediate

1 What is Kubernetes?

  1. What is Kubernetes?
  2. Why Kubernetes?
  3. Cluster architecture
  4. Control plane
  5. Worker node
  6. Summary - What is Kubernetes

2 Minikube

  1. What is Minikube?
  2. Installing Minikube
  3. minikube start
  4. minikube status
  5. minikube dashboard
  6. Summary - Minikube

3 kubectl basics

  1. What is kubectl?
  2. kubectl get
  3. kubectl describe
  4. kubectl apply
  5. kubectl delete
  6. Summary - kubectl

4 Pod

  1. What is a Pod?
  2. Pod YAML
  3. Creating a Pod
  4. Pod status
  5. Multi-container Pod
  6. Summary - Pod

5 Deployment

  1. What is a Deployment?
  2. Deployment YAML
  3. Replica count
  4. Rolling update
  5. Rollback
  6. Summary - Deployment

6 ReplicaSet

  1. What is a ReplicaSet?
  2. ReplicaSet YAML
  3. ReplicaSet selector
  4. Scaling
  5. Self-healing
  6. Summary - ReplicaSet

7 Service

  1. What is a Service?
  2. ClusterIP
  3. NodePort
  4. LoadBalancer
  5. Service selector
  6. Summary - Service

8 ConfigMap

  1. What is a ConfigMap?
  2. ConfigMap YAML
  3. Environment variable
  4. Mounting as a volume
  5. kubectl create configmap
  6. Summary - ConfigMap

9 Secret

  1. What is a Secret?
  2. Secret types
  3. Secret YAML
  4. Mounting a Secret
  5. kubectl create secret
  6. Summary - Secret

10 Namespace

  1. What is a Namespace?
  2. kubectl get namespaces
  3. Creating a Namespace
  4. The -n flag
  5. Default Namespace
  6. Summary - Namespace

11 Labels and selectors

  1. What is a label?
  2. Adding labels
  3. Label selector
  4. kubectl get -l
  5. Equality and set selectors
  6. Summary - Labels

12 Project: Multi-tier app

  1. Project design
  2. Database Deployment
  3. Web Deployment
  4. ConfigMap and Secret
  5. Putting it together - multi-tier

13 Troubleshooting

  1. kubectl logs
  2. kubectl exec
  3. kubectl describe pod
  4. CrashLoopBackOff
  5. Pending Pod
  6. Summary - Troubleshooting

14 Intermediate final

  1. Challenge - Pod YAML
  2. Challenge - Deployment
  3. Challenge - Service
  4. Challenge - ConfigMap
  5. Challenge - Intermediate project