Intro Guide to Dockerfile Best Practices

There are over one million Dockerfiles on GitHub today, but not all Dockerfiles are created equally. Efficiency is critical, and this blog series will cover five areas for Dockerfile best practices to help you write better Dockerfiles: incremental build time, image size, maintainability, security and repeatability. If you’re just beginning with Docker, this first blog post is for you! The next posts in the series will be more advanced.

Important note: the tips below follow the journey of ever-improving Dockerfiles for an example Java project based on Maven. The last Dockerfile is thus the recommended Dockerfile, while all intermediate ones are there only to illustrate specific best practices.

Incremental build time

In a development cycle, when building a Docker image, making code changes, then rebuilding, it is important to leverage caching. Caching helps to avoid running build steps again when they don’t need to.

Tip #1: Order matters for caching

However, the order of the build steps (Dockerfile instructions) matters, because when a step’s cache is invalidated by changing files or modifying lines in the Dockerfile, subsequent steps of their cache will break. Order your steps from least to most frequently changing steps to optimize caching.

Tip #2: Continue reading