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]>
52 lines
2.7 KiB
Markdown
52 lines
2.7 KiB
Markdown
# Images and Containers
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## The single most important distinction in this course
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**An image is a packaged, read-only ARTIFACT. A container is a RUNNING INSTANCE of an image.**
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This is exactly analogous to a program's executable file (the image) versus a running process
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of that program (the container) — a distinction ROOT 01's process module already gave you
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vocabulary for. You can run the SAME image many times, producing many independent containers,
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the same way you can run the same program multiple times as separate processes.
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## Layers: how an image is actually built
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An image is built from a stack of **layers**, each representing one change (install a package,
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copy in application code, set a configuration). Layers are cached and shared — if two images
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both start `FROM alpine:3.19`, they share that base layer on disk rather than duplicating it,
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which is why pulling a new image that shares layers with one you already have is often much
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faster than the total image size suggests.
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## Registries, repositories, and tags
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- **Registry** — a server that stores and distributes images (Docker Hub is the default public
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one; a company might run a private registry).
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- **Repository** — a named collection of related images (e.g. `nginx`).
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- **Tag** — a specific version within a repository (`nginx:alpine`, `nginx:1.25`, `nginx:latest`).
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`latest` is just a conventional tag name, not automatically "the newest" in any enforced sense
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— relying on it in production is a common, avoidable source of surprise.
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## The core commands, mapped to the model
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- **`docker pull <image>`** — download an image from a registry, without running it.
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- **`docker run <image>`** — create and start a NEW container from an image (pulls automatically
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if not already present locally).
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- **`docker stop <container>`** — gracefully stop a running container (its process, not the
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image).
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- **`docker rm <container>`** — delete a stopped container. This does NOT delete the image it
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was created from.
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## Instructor Notes
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**Lesson goal:** Land the image/container distinction as concretely as possible — nearly every
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later confusion in this course traces back to conflating the two.
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**Approximate timing:** 15 minutes read; 10 minutes live.
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**Common misconception to watch for:** using "image" and "container" interchangeably in casual
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speech — gently correct this early and often, since precise vocabulary here prevents real
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confusion later (e.g., "did you delete the container or the image?" matters).
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**Discussion question:** "If you run `docker run nginx:alpine` three times, how many images
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exist afterward? How many containers?" (Answer: 1 image, 3 containers — a good check before
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moving to the hands-on Lab.)
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