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:

• Katacoda
• Play with Kubernetes

Add a label to a node

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

   kubectl get nodes --show-labels
   

   The output is similar to this:

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

2. Chose one of your nodes, and add a label to it:

   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:

   kubectl get nodes --show-labels
   

   The output is similar to this:

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

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  affinity:
    nodeAffinity:
      requiredDuringSchedulingIgnoredDuringExecution:
        nodeSelectorTerms:
        - matchExpressions:
          - key: disktype
            operator: In
            values:
            - ssd            
  containers:
  - name: nginx
    image: nginx
    imagePullPolicy: IfNotPresent

1. Apply the manifest to create a Pod that is scheduled onto your chosen node:

   kubectl apply -f https://k8s.io/examples/pods/pod-nginx-required-affinity.yaml
   

2. Verify that the pod is running on your chosen node:

   kubectl get pods --output=wide
   

   The output is similar to this:

   NAME     READY     STATUS    RESTARTS   AGE    IP           NODE
   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.

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  affinity:
    nodeAffinity:
      preferredDuringSchedulingIgnoredDuringExecution:
      - weight: 1
        preference:
          matchExpressions:
          - key: disktype
            operator: In
            values:
            - ssd          
  containers:
  - name: nginx
    image: nginx
    imagePullPolicy: IfNotPresent

1. Apply the manifest to create a Pod that is scheduled onto your chosen node:

   kubectl apply -f https://k8s.io/examples/pods/pod-nginx-preferred-affinity.yaml
   

2. Verify that the pod is running on your chosen node:

   kubectl get pods --output=wide
   

   The output is similar to this:

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

What's next

Learn more about Node Affinity.