Docker Cookbook

Chapter 2. Image Creation and Sharing

2.0 Introduction

Quickly after discovering the basic principles of using Docker, you will want to create your own container images. Maybe you will want to package an existing application or you will want to build a new one from scratch leveraging Docker. This chapter is about creating container images and sharing them with others.

The first concept around creating images is that you can start a container using a base image and interactively make changes to it. Docker lets you keep those changes by committing them into a new image (see Recipe 2.1). Under the covers, Docker keeps track of the difference between your base image and your new image by creating a new image layer using the union filesystem being used. Sharing this new image is as easy as exporting it to a tar file and giving this tar file to others (see Recipe 2.2).

But making changes to a container manually and committing them to a new images is not highly reproducible and not automated. A better solution is to create a Dockerfile that will let Docker build the image automatically (see Recipe 2.3). You can go through creating a Dockerfile for a simple Python-based Flask application in Recipe 2.4, and in Recipe 2.5 you will learn the best practices to optimize this Dockerfile.

If you have used Vagrant and Packer before you will want to go through Recipe 2.7 and Recipe 2.8; this will help you embrace Docker and build Docker images by re-using your existing configuration management ...