Lab Solution Node Affinity Optional

This lab walks through practical Kubernetes node affinity tasks: inspecting node labels, labeling a node, creating deployments, and constraining pods to specific nodes using nodeAffinity. The steps below show the commands, minimal YAML snippets, and verification commands you can run in a cluster.

1) Count labels on node01

List labels on a node with either kubectl describe or kubectl get --show-labels. Example using --show-labels:

root@controlplane:~# kubectl get node node01 --show-labels
NAME    STATUS   ROLES    AGE   VERSION   LABELS
node01  Ready    <none>   14m   v1.20.0   beta.kubernetes.io/arch=amd64,kubernetes.io/hostname=node01,...

Or view the full label list with:

root@controlplane:~# kubectl describe node node01
# Look under the "Labels:" section in the output.

Count the labels shown. (In the environment used here the node shows six labels.)

2) Check the value of `beta.kubernetes.io/arch` on node01

You can scan the --show-labels output for the label or inspect kubectl describe output:

root@controlplane:~# kubectl get node node01 --show-labels
# Look for the 'beta.kubernetes.io/arch' label in the LABELS column.

In this cluster beta.kubernetes.io/arch=amd64.

3) Apply a label `color=blue` to node01

Add a label to the node using kubectl label:

root@controlplane:~# kubectl label node node01 color=blue
node/node01 labeled

Verify the label was applied:

root@controlplane:~# kubectl get node node01 --show-labels
NAME    STATUS   ROLES    AGE   VERSION   LABELS
node01  Ready    <none>   14m   v1.20.0   color=blue,beta.kubernetes.io/arch=amd64,...

4) Create a deployment named `blue` (nginx) with 3 replicas

Create the deployment:

root@controlplane:~# kubectl create deployment blue --image=nginx --replicas=3
deployment.apps/blue created

Before adding affinity, check which nodes could schedule the pods. Look for taints (if no taints, pods may schedule to any node that meets resource/constraint requirements):

root@controlplane:~# kubectl get nodes
NAME          STATUS   ROLES                AGE   VERSION
controlplane  Ready    control-plane,master 15m   v1.20.0
node01        Ready    <none>               14m   v1.20.0

root@controlplane:~# kubectl describe node node01 | grep Taints
Taints:         <none>

root@controlplane:~# kubectl describe node controlplane | grep Taints
Taints:         <none>

Because there are no taints, the scheduler could place the blue pods on either node by default.

5) Constrain `blue` deployment to node01 using nodeAffinity

Edit the blue Deployment and add a nodeAffinity rule under spec.template.spec.affinity.nodeAffinity so the scheduler only places pods on nodes with color=blue. Open the deployment for editing:

root@controlplane:~# kubectl edit deployment blue

Inside the Deployment’s Pod template, add the following YAML under spec.template.spec (maintain correct indentation relative to the existing manifest):

affinity:
  nodeAffinity:
    requiredDuringSchedulingIgnoredDuringExecution:
      nodeSelectorTerms:
      - matchExpressions:
        - key: color
          operator: In
          values:
          - blue

A minimal view of the relevant part of the updated Deployment spec:

spec:
  replicas: 3
  template:
    metadata:
      labels:
        app: blue
    spec:
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
            - matchExpressions:
              - key: color
                operator: In
                values:
                - blue
      containers:
      - name: nginx
        image: nginx

Save the edit and verify the pods are scheduled on node01:

root@controlplane:~# kubectl get pods -o wide -l app=blue
NAME                      READY   STATUS    RESTARTS   AGE   NODE
blue-xxxxx-yyyyy          1/1     Running   0          1m    node01
blue-xxxxx-zzzzz          1/1     Running   0          1m    node01
blue-xxxxx-aaaaa          1/1     Running   0          1m    node01

All blue pods are now placed on node01 as required.

When using operator: In you must provide one or more values. The node must have the exact label key/value pair to match.

6) Create a deployment named `red` (nginx) with 2 replicas and ensure it runs on the control plane node

The control plane node has the label node-role.kubernetes.io/master (no value). To match nodes that have the label regardless of its value, use the Exists operator. Recommended workflow: generate the Deployment YAML with a dry-run, edit it to add the affinity block, then create it. Generate YAML:

root@controlplane:~# kubectl create deployment red --image=nginx --replicas=2 --dry-run=client -o yaml > red.yaml

Edit red.yaml and add the nodeAffinity under spec.template.spec:

spec:
  replicas: 2
  template:
    metadata:
      labels:
        app: red
    spec:
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
            - matchExpressions:
              - key: node-role.kubernetes.io/master
                operator: Exists
      containers:
      - name: nginx
        image: nginx

Important: operator: Exists must be used without a values field. Create the deployment:

root@controlplane:~# kubectl create -f red.yaml
deployment.apps/red created

Verify the red pods are scheduled on the control plane node:

root@controlplane:~# kubectl get pods -o wide -l app=red
NAME                      READY   STATUS    RESTARTS   AGE   NODE
red-xxxxx-yyyyy           1/1     Running   0          30s   controlplane
red-xxxxx-zzzzz           1/1     Running   0          30s   controlplane

YAML indentation is significant. If you see errors like did not find expected key when creating from a file, check the spacing/indentation for the added affinity block relative to spec.template.spec.

Quick reference: common commands and affinity operators

Purpose	Command / YAML
List node labels	`kubectl get node node01 --show-labels`
Describe node	`kubectl describe node node01`
Add a label to a node	`kubectl label node node01 color=blue`
Create deployment	`kubectl create deployment blue --image=nginx --replicas=3`
Dry-run to file	`kubectl create deployment red --image=nginx --replicas=2 --dry-run=client -o yaml > red.yaml`
nodeAffinity key exists (no value)	`operator: Exists`
nodeAffinity exact match	`operator: In` with `values: ["blue"]`

You have now completed the lab tasks:

inspected node labels,
applied a node label,
created a deployment and constrained it to a specific node using nodeAffinity with In,
and created another deployment constrained to nodes that have a label using the Exists operator.

Introduction

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Mock Exams

Lab Solution Node Affinity Optional

1) Count labels on node01

2) Check the value of `beta.kubernetes.io/arch` on node01

3) Apply a label `color=blue` to node01

4) Create a deployment named `blue` (nginx) with 3 replicas

5) Constrain `blue` deployment to node01 using nodeAffinity

6) Create a deployment named `red` (nginx) with 2 replicas and ensure it runs on the control plane node

Quick reference: common commands and affinity operators

Links and References

Watch Video

​1) Count labels on node01

​2) Check the value of beta.kubernetes.io/arch on node01

​3) Apply a label color=blue to node01

​4) Create a deployment named blue (nginx) with 3 replicas

​5) Constrain blue deployment to node01 using nodeAffinity

​6) Create a deployment named red (nginx) with 2 replicas and ensure it runs on the control plane node

​Quick reference: common commands and affinity operators

​Links and References

Watch Video

1) Count labels on node01

2) Check the value of `beta.kubernetes.io/arch` on node01

3) Apply a label `color=blue` to node01

4) Create a deployment named `blue` (nginx) with 3 replicas

5) Constrain `blue` deployment to node01 using nodeAffinity

6) Create a deployment named `red` (nginx) with 2 replicas and ensure it runs on the control plane node

Quick reference: common commands and affinity operators

Links and References