Docker & Kubernetes · Module 02

Building Docker Images with Dockerfile

Write Dockerfiles, understand layers and the build cache, use CMD/ENTRYPOINT correctly and keep production images small with multi-stage builds.

Practice interactively →

What you will learn

• Build, tag and inspect the layers of an image from a Dockerfile
• Use FROM, RUN, WORKDIR, COPY, EXPOSE, ENV and ARG correctly
• Predict the command that runs when ENTRYPOINT, CMD and docker run arguments combine
• Shrink images and use the build cache well with multi-stage builds

Lessons

1. Dockerfile and image layers

   A Dockerfile is the recipe for an image; every instruction that changes the filesystem adds a layer on top of the base image.

2. The main Dockerfile instructions

   FROM, RUN, WORKDIR, COPY, EXPOSE, ENV and ARG — what each instruction does and the usual traps.

3. CMD and ENTRYPOINT

   ENTRYPOINT is the main program, CMD holds the default arguments; arguments after the image name replace CMD, not ENTRYPOINT.

4. Multi-stage builds and the build cache

   Split the build stage from the production stage so the final image only holds the artifact; order instructions to use the cache.