ced4568andClaude Sonnet 5
682ef2de47
Adds all 8 ROOT 04 modules (why containers exist, images & containers, Docker CLI, container networking, container storage, Dockerfile & image build, Docker Compose, containers → Kubernetes) — 43 activities, using the nested Docker Engine Phase 6D built and tested. Modules 1, 2, and 8 are conceptual (no lab by design) — the honest bridge module (M8) explicitly names what Kubernetes adds beyond what this course already taught, without re-teaching Kubernetes itself. Adds 5 new hands-on Docker scenarios plus 2 MCQs, all against the real nested Docker Engine: docker-cli-basics (run/exec/inspect a real container), docker-container-networking (a genuine "works internally, unreachable from host" port-publishing failure, diagnosed and fixed by recreating the container with the correct `-p` flag), docker-container-storage (a real destroy/recreate cycle proving named-volume persistence, not just described), docker-build-image (a real Dockerfile, a real build, a real custom image run), and docker-compose-multiservice (a real two-service Compose application with a real published port). All tested end-to-end via the real scenario-validation API, including negative tests. Wires rootnode-containers-assessment (2 required + 4 random-draw scenarios) using the existing Phase 3B assessment engine. This completes the entire ROOT_ Foundations sequence (ROOT 01-04) — see docs/PHASE6E_ROOT_FOUNDATIONS_COMPLETION.md. Co-Authored-By: Claude Sonnet 5 <[email protected]>
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Dockerfile and Image Build
A Dockerfile is a recipe for an image
Every image you've used so far (nginx:alpine, alpine:3.19) was itself BUILT from a
Dockerfile by someone else. This module teaches you to write your own.
The core instructions
FROM <image>— every Dockerfile starts by choosing a base image to build on top of. Almost nothing is built completely from scratch.WORKDIR <path>— sets the working directory for every instruction that follows it (and for the container's default working directory when it runs).COPY <host-path> <image-path>— copies files from your BUILD CONTEXT (the directory you rundocker buildfrom) into the image.RUN <command>— executes a command DURING the build, creating a new layer with its result (installing a package, for example).CMD <command>(conceptually) — sets the DEFAULT command a container runs when started from this image, if nothing else is specified.ENTRYPOINT <command>(conceptually) — similar toCMD, but harder to override atdocker runtime — the two are often combined (ENTRYPOINTas the fixed program,CMDas its default arguments).
Build context and .dockerignore
docker build -t mytag . — that final . is the build context: the directory Docker can
see and copy files FROM during the build. A .dockerignore file (same idea as .gitignore from
ROOT 03) excludes files from the build context — keeping large or irrelevant files (like a local
.git folder or dependency caches) out of your image and speeding up builds.
Layers, again
Each instruction in a Dockerfile creates one layer, cached individually. Docker reuses cached
layers for instructions that haven't changed since the last build — which is why the ORDER of
instructions matters for build speed: put things that change rarely (like FROM and installing
dependencies) before things that change often (like copying your actual application code), so a
small code change doesn't invalidate expensive earlier layers.
Instructor Notes
Lesson goal: Give students enough Dockerfile literacy to write a real, small, working image — not exhaustive coverage of every possible instruction.
Approximate timing: 18 minutes read; 10 minutes live.
Common misconception to watch for: copying application code before installing dependencies — reinforce the "changes-rarely-first" layer-ordering principle with a concrete example.
Demo idea: build the same Dockerfile twice with no changes, showing the second build using
fully cached layers (CACHED in the output) and finishing almost instantly.