How to update a container image in a deployment?

Updating a Container Image in a Kubernetes Deployment

In the world of Kubernetes, managing and updating container images is a crucial aspect of application deployment and maintenance. When you need to update the container image used in a Kubernetes deployment, there are a few steps you can follow to ensure a smooth and efficient process.

Understanding Kubernetes Deployments

A Kubernetes deployment is a declarative way to manage the lifecycle of a set of replicated pods. It ensures that a specified number of pod replicas are running at any given time, and it provides mechanisms for rolling out changes, such as new container images, to those pods.

Updating the Container Image

To update the container image used in a Kubernetes deployment, you can follow these steps:

Identify the Deployment: First, you need to identify the Kubernetes deployment that you want to update. You can do this using the kubectl get deployments command.

Update the Container Image: Once you have identified the deployment, you can update the container image used in the deployment. You can do this by editing the deployment configuration file or by using the kubectl set image command.

# Update the container image using kubectl set image
kubectl set image deployment/my-deployment container-name=new-image:v2

Alternatively, you can edit the deployment configuration file directly and update the spec.template.spec.containers[].image field.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
      - name: container-name
        image: new-image:v2

Apply the Changes: After updating the container image, you need to apply the changes to the Kubernetes cluster. You can do this by running the kubectl apply command.
```
kubectl apply -f deployment.yaml
```
Alternatively, if you used the kubectl set image command, the changes will be applied automatically.
Monitor the Rollout: Kubernetes will automatically start rolling out the changes to the deployment. You can monitor the progress of the rollout using the kubectl rollout status command.
```
kubectl rollout status deployment/my-deployment
```
This command will display the status of the rollout, including the number of updated, available, and total replicas.

Understanding the Rollout Process

When you update the container image in a Kubernetes deployment, Kubernetes will perform a rolling update. This means that it will gradually replace the old pods with new pods running the updated container image, ensuring that the application remains available during the update process.

The rolling update process is controlled by the deployment strategy, which can be configured in the deployment specification. The two main strategies are:

RollingUpdate: This is the default strategy, where Kubernetes will gradually replace the old pods with new pods, ensuring that a certain number of pods are available at all times.
Recreate: This strategy will first terminate all the old pods and then create new pods with the updated container image. This approach results in downtime during the update process.

You can visualize the rollout process using a Mermaid diagram:

graph LR A[Old Pods] --> B[New Pods] B --> C[Updated Deployment] A --> C C --> D[Rollout Complete]

In this diagram, the old pods are gradually replaced by the new pods running the updated container image, until the entire deployment is updated.

By following these steps, you can efficiently update the container image used in a Kubernetes deployment, ensuring that your application remains available and up-to-date.