Although Java originally promised write once, run anywhere, it failed to fully deliver on that promise. As developers, we can develop, test, and build our applications into WAR or executable JAR files and then toss them over the wall to a Java application server and Java runtime that we have no control over, giving us zero confidence that the application will behave the same as when we tested it.

Containers fulfill the write-once, run anywhere promise that Java wasn't able to, by packaging the runtime and even the operating system along with our application, giving greater control and confidence that the application will function the same anywhere it is run. Additionally, containers afford several other benefits, including easy scaling, efficiency in terms of resource utilization, and security by isolating containers from their host system and from other containers.

While deploying Spring applications in containers has always been possible, Spring Boot 2.3 makes it easier to containerize our applications and run them in container architectures such as Kubernetes. Spring Boot 2.3's support for containerization includes two options: Creating containers based on buildpacks or using layers as a means of modularizing and reducing the size of our application deployments. Moreover, new components in the Spring ecosystem can make your Spring applications Kubernetes-savvy so that they can take advantage of what a containerized architecture has to offer.

In this example-driven session, we're going to look at how to create and deploy Spring applications as container images and deploy them into a Kubernetes cluster. Along the way, we'll also get to know a few of the most useful tools that a Spring developer can employ in their development workflow when building containerized Spring applications. And we'll look at how components of the Spring ecosystem can work with your Spring applications to enable them to thrive in a Kubernetes cluster.