Assign Pods to Nodes using Node Affinity

This page shows how to assign a Kubernetes Pod to a particular node using Node Affinity in a Kubernetes cluster.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

Your Kubernetes server must be at or later than version v1.10. To check the version, enter kubectl version.

Add a label to a node

  1. List the nodes in your cluster, along with their labels:

    1. kubectl get nodes --show-labels

    The output is similar to this:

    1. NAME STATUS ROLES AGE VERSION LABELS
    2. worker0 Ready <none> 1d v1.13.0 ...,kubernetes.io/hostname=worker0
    3. worker1 Ready <none> 1d v1.13.0 ...,kubernetes.io/hostname=worker1
    4. worker2 Ready <none> 1d v1.13.0 ...,kubernetes.io/hostname=worker2
  2. Choose one of your nodes, and add a label to it:

    1. kubectl label nodes <your-node-name> disktype=ssd

    where <your-node-name> is the name of your chosen node.

  3. Verify that your chosen node has a disktype=ssd label:

    1. kubectl get nodes --show-labels

    The output is similar to this:

    1. NAME STATUS ROLES AGE VERSION LABELS
    2. worker0 Ready <none> 1d v1.13.0 ...,disktype=ssd,kubernetes.io/hostname=worker0
    3. worker1 Ready <none> 1d v1.13.0 ...,kubernetes.io/hostname=worker1
    4. worker2 Ready <none> 1d v1.13.0 ...,kubernetes.io/hostname=worker2

    In the preceding output, you can see that the worker0 node has a disktype=ssd label.

Schedule a Pod using required node affinity

This manifest describes a Pod that has a requiredDuringSchedulingIgnoredDuringExecution node affinity,disktype: ssd. This means that the pod will get scheduled only on a node that has a disktype=ssd label.

pods/pod-nginx-required-affinity.yaml Assign Pods to Nodes using Node Affinity - 图1

  1. apiVersion: v1
  2. kind: Pod
  3. metadata:
  4. name: nginx
  5. spec:
  6. affinity:
  7. nodeAffinity:
  8. requiredDuringSchedulingIgnoredDuringExecution:
  9. nodeSelectorTerms:
  10. - matchExpressions:
  11. - key: disktype
  12. operator: In
  13. values:
  14. - ssd
  15. containers:
  16. - name: nginx
  17. image: nginx
  18. imagePullPolicy: IfNotPresent
  1. Apply the manifest to create a Pod that is scheduled onto your chosen node:

    1. kubectl apply -f https://k8s.io/examples/pods/pod-nginx-required-affinity.yaml
  2. Verify that the pod is running on your chosen node:

    1. kubectl get pods --output=wide

    The output is similar to this:

    1. NAME READY STATUS RESTARTS AGE IP NODE
    2. nginx 1/1 Running 0 13s 10.200.0.4 worker0

Schedule a Pod using preferred node affinity

This manifest describes a Pod that has a preferredDuringSchedulingIgnoredDuringExecution node affinity,disktype: ssd. This means that the pod will prefer a node that has a disktype=ssd label.

pods/pod-nginx-preferred-affinity.yaml Assign Pods to Nodes using Node Affinity - 图2

  1. apiVersion: v1
  2. kind: Pod
  3. metadata:
  4. name: nginx
  5. spec:
  6. affinity:
  7. nodeAffinity:
  8. preferredDuringSchedulingIgnoredDuringExecution:
  9. - weight: 1
  10. preference:
  11. matchExpressions:
  12. - key: disktype
  13. operator: In
  14. values:
  15. - ssd
  16. containers:
  17. - name: nginx
  18. image: nginx
  19. imagePullPolicy: IfNotPresent
  1. Apply the manifest to create a Pod that is scheduled onto your chosen node:

    1. kubectl apply -f https://k8s.io/examples/pods/pod-nginx-preferred-affinity.yaml
  2. Verify that the pod is running on your chosen node:

    1. kubectl get pods --output=wide

    The output is similar to this:

    1. NAME READY STATUS RESTARTS AGE IP NODE
    2. nginx 1/1 Running 0 13s 10.200.0.4 worker0

What’s next

Learn more about Node Affinity.