What is a Dockerfile and how do you use it to create a Docker image?

A Dockerfile is a text file that contains all the commands, in order, needed to build a customized docker image on top of a basic docker image. The docker build command processes this file and generates a docker image in your local image cache, which you can then run or push to a repository. You can specify the name of your custom docker image with the -t tag. The Dockerfile syntax and instructions are documented at Dockerfile reference1.