Docker images are basically filesystems bundled with parameters to use at runtime. The filesystem is usually a small part of a Linux Userland, with enough files to start the desired process. Docker provides tooling to build these images, generally based on very small, preexisting base images. The tooling uses a Dockerfile as the input, which is a plain text file with directives. This file is parsed by the docker build command, and we can parse it via the docker_image module. The remaining examples will be from a CentOS 7 virtual machine using Docker version 1.13.1, with the cowsay and nginx packages added, so that running the container will provide a web server that will display something from cowsay.
First, we'll need a ...
