Kubernetes: Up and Running, 3rd Edition

Chapter 10. Deployments

So far, you have seen how to package your applications as containers, create replicated sets of containers, and use Ingress controllers to load balance traffic to your services. You can use all of these objects (Pods, ReplicaSets, and Services) to build a single instance of your application. However, they do little to help you manage the daily or weekly cadence of releasing new versions of your application. Indeed, both Pods and ReplicaSets are expected to be tied to specific container images that don’t change.

The Deployment object exists to manage the release of new versions. Deployments represent deployed applications in a way that transcends any particular version. Additionally, Deployments enable you to easily move from one version of your code to the next. This “rollout” process is specifiable and careful. It waits for a user-configurable amount of time between upgrading individual Pods. It also uses health checks to ensure that the new version of the application is operating correctly and stops the deployment if too many failures occur.

Using Deployments, you can simply and reliably roll out new software versions without downtime or errors. The actual mechanics of the software rollout performed by a Deployment are controlled by a Deployment controller that runs in the Kubernetes cluster itself. This means you can let a Deployment proceed unattended and it will still operate correctly and safely. This makes it easy to integrate Deployments with numerous ...