Building the recipes for images

All instructions should be saved in a text file, named by default Dockerfile.

Basic instructions

Each row in the recipe corresponds to a layer of the final image.

FROM: parent image. Typically, an operating system but you can also use an image of other parties as starting point. This instruction creates the base layer.

FROM ubuntu:18.04

RUN: the command to execute inside the image filesystem.
Think about it this way: every RUN line is essentially what you would run to install programs on a freshly installed Ubuntu OS. This command will be executed as root in the container.

RUN apt install wget

A basic recipe:

FROM ubuntu:18.04

RUN apt update && apt -y upgrade
RUN apt install -y wget