Dockerfile

As you will remember from Chapter 1, Introduction to Docker, the Dockerfile is kind of a recipe to build an image. It's a plain text file containing instructions which are executed by Docker in the order they are placed. Each Dockerfile has a base image that the Docker engine will use to build upon. A resulting image will be a specific state of a file system: a read-only, frozen immutable snapshot of a live container, composed of layers representing changes in the filesystem at various points in time.

The image creation flow in Docker is pretty straightforward and consists basically of two steps:

1. First, you prepare a text file named Dockerfile, which contains a series of instructions on how to build the image. The set of instructions you can use in the Dockerfile is not very broad, but sufficient to fully instruct Docker how to create an image.
2. Next, you execute the docker build command to create a Docker image based on the Dockerfile that you have just created. The docker build...