Docker flashcards

Pack an app with everything it needs, run it the same on a laptop, in CI and in production.

Learn

Beginner friendly, starts from zero

CardsCheatsheetTips and tricks

DockerStart from zero · 1 of 12

What is Docker, in one plain sentence?

Think of the answer, then tap

A tool that packs an app together with everything it needs to run, so it works the same on any computer.

A lunch box that holds the whole meal, plate and spoon included.

Space turn over · K got it · J again · ← back

All topics

Docker at a glance

Docker packs an app with everything it needs, so it runs the same on every computer.

Like a shipping container: one standard box that any ship or truck can carry, whatever is inside.

Words you will meet

Image: The packed, frozen app with everything it needs
Container: One running copy of an image
Host: The computer Docker is running on
Port: A numbered door that lets other programs reach the app
Dockerfile: A text file with the steps to build an image
Tag: A version label on an image, like 2.4.1
Registry: An online shelf where images are stored and shared
Volume: A storage folder outside the container that keeps your data safe

The steps

1. Start from zero (12 cards): What Docker is, the key words in plain English, and your first container.
2. Core basics (16 cards): Images, containers, ports, logs and your first Dockerfile, with the mistakes beginners really make.
3. Next steps (16 cards): Volumes, layer caching, .dockerignore, Compose stacks, networking and health checks used every week.
4. Go deeper (17 cards): Small hardened images, BuildKit, multi-arch builds, signals, supply chain, CI caching and the kernel features underneath.

All 12 cards in Start from zero

What is Docker, in one plain sentence?: A tool that packs an app together with everything it needs to run, so it works the same on any computer.
What problem did people have before Docker?: An app worked on one person's laptop and broke on another because a tool or version was different. Setting up each new computer took hours of careful steps.
Where do you already meet Docker without knowing it?: Many websites and apps you use every day, from shops to banking, run inside Docker-style containers on big server computers in data centres.
What is an everyday picture for images and containers?: Shipping containers. Every box has the same shape, so any ship or truck can carry it, whatever is inside. Docker does the same for apps.
What are a server, a terminal and a command?: A server is a computer that runs apps for other people, usually far away. A terminal is a text window where you type a command, a short line telling the computer what to do.
What do image and container mean?: An image is the packed, frozen app: the recipe plus all ingredients. A container is one running copy of an image. One image can start many containers.
What are the host, a process and a port?: The host is the computer Docker runs on. A process is one program that is running right now. A port is a numbered door, like 8080, that lets other programs talk to it.
What are a Dockerfile, a tag and a registry?: A Dockerfile is a text file of steps for building an image. A tag is a version label on an image, like 2.4. A registry is an online shelf where images are stored and shared.
What is a volume, and why does it matter?: A volume is a safe storage folder that lives outside the container. Throw a container away and its own files go too, but the volume keeps your data.
What do you need before you start?: A computer with Docker Desktop installed (free for personal use) and a terminal. You do not need to know how servers work yet.
What does your first Docker command do?: docker run starts a container from the hello-world image. Docker downloads the image the first time, prints a welcome message, and the container stops.
What will you be able to do after this topic?: Run any app from an image, open it in your browser through a port, write a Dockerfile for your own app, keep data safe in a volume and share your image through a registry.

Docker cheatsheet

Containers

docker run -d --name api -p 127.0.0.1:8000:8000 IMG Run in background, local port only
docker run --rm -it IMG sh Throwaway shell, removed on exit
docker ps -a --format 'table {{.Names}}\t{{.Status}}' All containers with status
docker logs -f --since 10m api Follow recent logs
docker exec -it api sh Shell in a running container
docker stats --no-stream CPU and memory per container
docker rm -f api Kill and remove

Build and ship

docker build -t app:1.4.0 . Build from Dockerfile in this folder
docker build --progress=plain --no-cache . Full log, ignore cache
docker buildx build --platform linux/amd64,linux/arm64 --push Multi-arch image
docker build --secret id=npmrc,src=~/.npmrc . Pass a build secret safely
docker tag app:1.4.0 ghcr.io/acme/app:1.4.0 Name for a registry
docker push ghcr.io/acme/app:1.4.0 Upload to registry
docker buildx imagetools inspect IMG Digests and platforms

Dockerfile

FROM node:24-slim AS build Named build stage
COPY package*.json ./ Manifests first for caching
RUN --mount=type=cache,target=/root/.npm npm ci Reuse download cache
COPY --from=build /app/dist ./dist Take output from a stage
COPY --chown=10001 . . Copy owned by the app user
USER 10001 Drop root
HEALTHCHECK CMD curl -fsS localhost:8000/health Report real health
CMD ["node", "server.js"] Exec form, gets signals

Compose

docker compose up -d --build Rebuild and start the stack
docker compose watch Sync or rebuild on file change
docker compose logs -f api Follow one service
docker compose exec db psql -U app Run a tool in a service
docker compose --profile dev up Include optional dev services
docker compose config Show the merged final config
docker compose down -v Stop and delete volumes too

Inspect and clean

docker system df Disk used by type
docker image inspect IMG --format '{{.Config.User}}' Read one config field
docker history --no-trunc IMG Layers and their commands
docker builder prune --filter until=72h Drop old build cache
docker image prune -a Remove unused images
docker scout cves IMG List known vulnerabilities