The Dockerfile

Each Docker image is defined by a Dockerfile, that describes what is in the image and how containers created from it should be built.

The Dockerfile is simply a text document, containing all the commands that would be issued on the command-line to build an image - in short, the Dockerfile defines an environment.

The Dockerfile is built automatically, and populated with appropriate commands (see below). However, you can also add any commands you wish to the Dockerfile, for example to install system packages, or to configure the environment.

Important

The Dockerfile executes its commands in sequence. This means that commands to install Node (for example) must come before commands to run Node packages.