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:

    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. Choose 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.

pods/pod-nginx-required-affinity.yaml
apiVersion:v1kind:Podmetadata:name:nginxspec:affinity:nodeAffinity:requiredDuringSchedulingIgnoredDuringExecution:nodeSelectorTerms:- matchExpressions:- key:disktypeoperator:Invalues:- ssd containers:- name:nginximage:nginximagePullPolicy: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.

pods/pod-nginx-preferred-affinity.yaml
apiVersion:v1kind:Podmetadata:name:nginxspec:affinity:nodeAffinity:preferredDuringSchedulingIgnoredDuringExecution:- weight:1preference:matchExpressions:- key:disktypeoperator:Invalues:- ssd containers:- name:nginximage:nginximagePullPolicy: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.

Last modified August 24, 2023 at 6:38 PM PST: Use code_sample shortcode instead of code shortcode (e8b136c3b3)