Phase 2Beginner3 of 11 in Docker

Dockerfile Mastery

Writing your own images — instructions, layers, caching, and the habits that separate a working Dockerfile from a good one.

So far you've only run images someone else built. This phase is about writing your OWN Dockerfile — the recipe Docker follows to build an image — and understanding exactly why it's structured the way it is.

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5 topics ~69 min 8 code blocks & diagrams

Start with the first topic

2.1

Your First Dockerfile

A Dockerfile is a plain-text recipe, read top to bottom, where each instruction produces exactly one new layer in the resulting image.

14 min 2 code practice

2.2

Layers & the Build Cache

Every Dockerfile instruction creates a cacheable layer, and the ORDER you write instructions in is the single biggest lever on how fast your builds are.

14 min 1 diagram 1 code practice

2.3

Build Context & .dockerignore

Everything in your build context gets sent to the Docker daemon before the build even starts — an unfiltered context silently slows every single build and can leak secrets into your image.

13 min 1 code practice

2.4

Dockerfile Best Practices

A checklist of habits that separate a Dockerfile a senior engineer would approve in code review from one that 'just works' on your laptop.

14 min 1 code practice

2.5

ENTRYPOINT vs CMD, and ARG vs ENV

Four instructions that look interchangeable until an interview (or a 2am incident) asks you to explain the exact difference — CMD is a default you can override, ENTRYPOINT usually isn't, ARG only exists at build time, ENV lives on into the running container.