Understand Deployments and how to perform rolling updates

Context: CKAD certification objective.

Understand Deployments and how to perform rolling updates

Understanding Deployments and performing rolling updates are crucial skills for the Certified Kubernetes Application Developer (CKAD) certification. Deployments are a Kubernetes resource that provides a declarative way to manage the lifecycle of a set of pods. Rolling updates allow you to update your application while minimizing downtime. Here's an overview of Deployments and how to perform rolling updates:

1. Deployments in Kubernetes:

   • A Deployment manages a ReplicaSet, which ensures that a specified number of pod replicas are running at any given time.
   • Deployments allow you to define the desired state of your application, including the number of replicas, the container image, environment variables, and other configuration parameters.
   • By using Deployments, you can easily scale your application, perform rolling updates, rollbacks, and manage the overall lifecycle of your application.

2. Performing Rolling Updates: Rolling updates allow you to update your application in a controlled manner, replacing old instances with new ones gradually. This minimizes the impact on the availability of your application. Here's how to perform rolling updates with Deployments:

   • Update the Deployment: Make the necessary changes to your Deployment configuration, such as updating the container image, environment variables, or other specifications.

   • Apply the Changes: Use the kubectl apply command to apply the updated Deployment configuration. For example:

     kubectl apply -f deployment.yaml

   • Monitor the Update Progress: You can monitor the progress of the rolling update using the kubectl rollout status command. It shows the current status of the Deployment and provides information about the ongoing update. For example:

     kubectl rollout status deployment <deployment-name>

   • Rollout Strategies: Kubernetes provides different strategies for rolling updates:

     • Recreate: The old pods are terminated before new pods are created. This strategy results in a brief downtime during the update.
     • RollingUpdate: This is the default strategy. It gradually replaces the old pods with new ones. You can specify the maximum number of pods to be unavailable (maxUnavailable) and the maximum number of new pods created (maxSurge) during the update.

   • Rollback Changes: If the rolling update encounters issues, you can roll back to the previous version using the kubectl rollout undo command. For example:

     kubectl rollout undo deployment <deployment-name>

   • Fine-grained Control: You can customize the rolling update behavior by modifying the Deployment's update strategy and configuring parameters like maxUnavailable and maxSurge. This allows you to control the number of pods available during the update and the rate of creating new pods.

Understanding Deployments and knowing how to perform rolling updates is essential for managing the lifecycle of your applications in Kubernetes. Practice working with Deployments, updating configurations, monitoring the update progress, and rolling back changes to gain confidence in these concepts and fulfill the requirements of the CKAD certification.