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Control plane

Learn the control plane components.

The control plane

The four main components of the control plane:

  • kube-apiserver: the REST API; all reads/writes go through it.
  • etcd: the distributed key-value database holding the cluster state.
  • kube-scheduler: picks a node for new pods.
  • kube-controller-manager: runs controller loops that move the actual state toward the desired state.
$ kubectl get pods -n kube-system
NAME                                    READY   STATUS
etcd-control-plane                      1/1     Running
kube-apiserver-control-plane            1/1     Running
kube-controller-manager-control-plane   1/1     Running
kube-scheduler-control-plane            1/1     Running

Component health

The API server has its own health endpoints. They can be read directly with kubectl get --raw; kubectl cluster-info shows the API address:

$ kubectl cluster-info
Kubernetes control plane is running at https://192.168.49.2:8443
CoreDNS is running at https://192.168.49.2:8443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
$ kubectl get --raw='/readyz?verbose' | tail -2
[+]etcd ok
readyz check passed

Practice Inspect the control plane

Write two commands: show the cluster information; list the pods in the kube-system namespace.

Starter code

terminal
# buraya yaz

Sample solution

terminal
kubectl cluster-info
kubectl get pods -n kube-system

Expected output

Kubernetes control plane is running at https://192.168.49.2:8443
NAME                               READY   STATUS    RESTARTS   AGE
etcd-minikube                      1/1     Running   0          2d
kube-apiserver-minikube            1/1     Running   0          2d

Questions and answers

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

1 Where is the whole state of the cluster stored?

  • On the worker nodes' disks
  • In the kubectl configuration
  • etcd Correct answer
  • kube-scheduler

Explanation: If etcd is lost, the cluster's definition is lost too; that's why it's backed up.

2 List the pods of the system components.

Question 
kubectl get pods -n ____
Answer 
kubectl get pods -n kube-system

Explanation: System components are in the kube-system namespace.

3 Match the components.

Term Meaning
kube-apiserver REST API
etcd State database
kube-scheduler Node selection
controller-manager Controller loops

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