How to Update Deployment in Kubernetes: Step-by-Step Guide

To update a deployment in Kubernetes, use the kubectl apply -f command with an updated deployment YAML file or use kubectl set image to change the container image directly. Kubernetes will then perform a rolling update to replace old pods with new ones without downtime.

Syntax

There are two common ways to update a deployment in Kubernetes:

• Using a YAML file: Update the deployment manifest file and run kubectl apply -f deployment.yaml.
• Using kubectl set image: Change the container image directly with kubectl set image deployment/DEPLOYMENT_NAME CONTAINER_NAME=NEW_IMAGE.

Kubernetes will then perform a rolling update, replacing pods gradually to avoid downtime.

bash

kubectl apply -f deployment.yaml

kubectl set image deployment/my-deployment my-container=my-image:tag

Example

This example shows how to update the container image of a deployment named nginx-deployment from nginx:1.14.2 to nginx:1.16.1 using kubectl set image. Kubernetes will roll out the new pods with the updated image.

bash

kubectl set image deployment/nginx-deployment nginx=nginx:1.16.1
kubectl rollout status deployment/nginx-deployment

Output

deployment "nginx-deployment" image updated
Waiting for deployment "nginx-deployment" rollout to finish: 2 of 3 updated replicas are available...
deployment "nginx-deployment" successfully rolled out

Common Pitfalls

Common mistakes when updating deployments include:

• Not specifying the correct container name in kubectl set image, causing no update.
• Forgetting to check rollout status, missing failed updates.
• Using kubectl apply with an incorrect or incomplete YAML file, which can cause unintended changes.
• Not having proper permissions to update the deployment.

Always verify the deployment status after updating to ensure the update succeeded.

bash

kubectl set image deployment/nginx-deployment wrong-container=nginx:1.16.1
# This will not update the image because the container name is incorrect

# Correct way:
kubectl set image deployment/nginx-deployment nginx=nginx:1.16.1

Quick Reference

Command	Description
kubectl apply -f deployment.yaml	Update deployment using updated YAML manifest
kubectl set image deployment/DEPLOYMENT_NAME CONTAINER_NAME=NEW_IMAGE	Update container image directly
kubectl rollout status deployment/DEPLOYMENT_NAME	Check rollout status of deployment
kubectl rollout undo deployment/DEPLOYMENT_NAME	Rollback to previous deployment version

Key Takeaways

Use kubectl apply with updated YAML or kubectl set image to update deployments.

Kubernetes performs rolling updates to avoid downtime during deployment changes.

Always check rollout status to confirm the update succeeded.

Specify the correct container name when updating images with kubectl set image.

Use kubectl rollout undo to rollback if the update causes issues.