Update a Container Image With Rolling Update in Kubernetes

This blog post will show you how to update a container image in a Kubernetes cluster using a rolling update strategy.

Rolling Update

The rolling update feature allows us to update a Kubernetes deployment without effecting the workloads and gradually replace pods with a new image.

Below, you can see the code block (strategy) that controls a rolling update. maxSurge control how many new pods with the new image will be added to the deployment while maxUnavailable control how many pods will be deleted.

strategy:
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 1
    type: RollingUpdate 

Configuration

Below, you can see the deployment file with all the configuration blocks, including the strategy block that controls a rolling update.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 2
  selector:
    matchLabels:
      app: nginx
  strategy:
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 1
    type: RollingUpdate    
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.19.7
        ports:
        - containerPort: 80

To deploy a new image, I will change the container image version and run the deployment using the following line.

kubectl apply -f main.yaml

To check the deployment status, I will run the rollout status with the deployment name, as shown below.

kubectl rollout status deployments nginx-deployment

The output below shows how a rolling update control the process of updating and image.

Waiting for deployment "nginx-deployment" rollout to finish: 1 old replicas are pending termination…
 Waiting for deployment "nginx-deployment" rollout to finish: 1 old replicas are pending termination…
 Waiting for deployment "nginx-deployment" rollout to finish: 1 old replicas are pending termination…
 Waiting for deployment "nginx-deployment" rollout to finish: 1 of 2 updated replicas are available…
 deployment "nginx-deployment" successfully rolled out

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