Introduction to Containerization

Objectives

In this chapter, you will understand the typical workflow to build an application into a container image. This process is called containerization, and the resulting application is called a containerized application.

We’ll use Docker to containerize the application (i.e., create the container image), and the steps that will be followed are not specific to the use of Kubernetes. In fact, we’ll not use Kubernetes in this chapter. However, it’s a vital part of a typical Kubernetes workflow, and we’ll deploy the containerized app to Kubernetes in the following chapters.

Docker and Kubernetes: Let’s clear up the confusion about Kubernetes supposedly dropping support for Docker. Kubernetes stopped using Docker as a container runtime in version 1.24. This means Kubernetes 1.24 and later do not use Docker to start and stop containers. However, apps containerized by Docker still work on Kubernetes and probably make up the majority of apps running on Kubernetes. This is because Kubernetes and Docker both implement Open Container Initiative (OCI) standards.

If you’re already familiar with containerizing apps, skip this chapter. There’s a pre-created image on Docker Hub that you can use.