This document covers recommended best practices and methods for building efficient images.
Docker builds images automatically by reading the instructions from a Dockerfile -- a text file that contains all commands, in order, needed to build a given image.
A Dockerfile adheres to a specific format and set of instructions which you can find at Dockerfile reference.
A Docker image consists of read-only layers each of which represents a Dockerfile instruction. The layers are stacked and each one is a delta of the changes from the previous layer. Consider this Dockerfile:
原文：https://www.cnblogs.com/panpanwelcome/p/9269980.html