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.