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By default, your Kubernetes Cluster will not schedule pods on the control-plane node for security reasons. It is recommended you keep it this way, but for test environments you may want to schedule Pods on control-plane node to maximize resource usage.

If you want to be able to schedule pods on the Kubernetes control-plane node, you need to remove a taint on the master nodes.

kubectl taint nodes --all

The output will look something like:

node/ untainted
taint "" not found
taint "" not found
taint "" not found

This will remove the taint from any nodes that have it, including the control-plane node, meaning that the scheduler will then be able to schedule pods everywhere.

Testing Pod Scheduling on Kubernetes Control plane node(s)

I have a cluster with three worker nodes and one control plane node.

$ kubectl get nodes
NAME                                STATUS   ROLES    AGE   VERSION   Ready    master   12h   v1.17.0     Ready    <none>   12h   v1.17.0     Ready    <none>   12h   v1.17.0     Ready    <none>   9h    v1.17.0

Create a demo namespace:

kubectl create namespace demo

Will create a deployment with 5 replicas.

$ vim nginx-deployment.yaml

It has the data below:

apiVersion: apps/v1
kind: Deployment
  name: nginx
  namespace: demo
    app: nginx
    color: green
  replicas: 5
      app: nginx
        app: nginx
        color: green
        - name: nginx
          image: nginx:latest
          imagePullPolicy: IfNotPresent
            - name: http
              protocol: TCP
              containerPort: 80
              cpu: "200m"
              memory: "256Mi"
              cpu: 100m
              memory: 128Mi
apiVersion: v1
kind: Service
  name: nginx-demo-service
  namespace: demo
    - port: 80
      targetPort: 80
      protocol: TCP
    app: nginx
  sessionAffinity: None
  type: NodePort

Apply manifest:

$ kubectl apply -f nginx-deployment.yaml

Check if a pod is scheduled to the control node plane.

$ kubectl get pods -n demo -o wide
NAME                     READY   STATUS    RESTARTS   AGE   IP                NODE                                NOMINATED NODE   READINESS GATES
nginx-675bf5bc87-666jg   1/1     Running   0          17m                
nginx-675bf5bc87-mc6px   1/1     Running   0          17m              
nginx-675bf5bc87-v5q87   1/1     Running   0          17m                
nginx-675bf5bc87-vctqm   1/1     Running   0          17m                
nginx-675bf5bc87-w5pmh   1/1     Running   0          17m                

We can see there is a pod in master node. Confirm service is live.

$ kubectl get svc -n demo
NAME            TYPE       CLUSTER-IP     EXTERNAL-IP   PORT(S)        AGE
nginx-service   NodePort   <none>        80:31098/TCP   21m

Since we’re using NodePort, we should be able to access the service on any cluster node IP on port 31098.

We can now clean demo objects.

$ kubectl delete -f nginx-deployment.yaml
deployment.apps "nginx" deleted
service "nginx-service" deleted

$ kubectl get pods,svc -n demo
No resources found in demo namespace.

That’s all on how to Schedule Pods on Kubernetes Control plane Node.

More guides:

How To Join new Kubernetes Worker Node to an existing Cluster

Deploy Kubernetes Cluster on CentOS 7 / CentOS 8 With Ansible and Calico CNI

How To Deploy Metrics Server to Kubernetes Cluster

Install and Use Helm 3 on Kubernetes Cluster

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