Docker: cheat sheet

The commands that cover 95% of daily container work. Bookmark it. Deep dives: Docker for beginners, writing a Dockerfile and docker compose.

Containers

Images

docker images                    # list images
docker build -t myapp:1.0 .      # build from a Dockerfile
docker pull postgres:16          # download
docker tag myapp:1.0 myapp:latest
docker push registry/myapp:1.0   # push to a registry
docker rmi <image>               # remove an image
docker history myapp:1.0         # layers and their sizes

Dockerfile - the essentials

FROM node:22-alpine
WORKDIR /app
COPY package*.json ./           # dependencies first - for layer caching
RUN npm ci --omit=dev
COPY . .
EXPOSE 3000
USER node                       # not root in production
CMD ["node", "server.js"]

Order matters: rarely-changing things go higher. Details: writing a Dockerfile.

docker compose

docker compose up -d             # bring the stack up, detached
docker compose down              # stop and remove
docker compose down -v           # + remove volumes (careful!)
docker compose ps                # service status
docker compose logs -f <service> # logs of one service
docker compose exec <service> sh # shell into a service
docker compose build --no-cache  # rebuild from scratch
docker compose pull              # update images

Volumes and data

docker volume ls
docker volume create mydata
docker run -v mydata:/var/lib/postgresql/data postgres:16   # named volume
docker run -v $(pwd):/app node:22                            # bind mount (host code)
docker volume rm mydata
docker volume prune              # remove unused volumes

Networks

docker network ls
docker network create mynet
docker run --network mynet --name db postgres:16    # containers reach each other by name
docker network inspect mynet

Debugging

docker inspect <id>              # full metadata (JSON)
docker inspect -f '{% raw %}{{.State.Status}}{% endraw %}' <id>   # one field
docker logs --tail 100 <id>      # last 100 lines
docker cp <id>:/app/log.txt .    # copy a file out of a container
docker diff <id>                 # what changed in the filesystem
docker top <id>                  # processes inside

Cleanup (reclaim space)

docker system df                 # how much is used
docker container prune           # remove stopped containers
docker image prune               # remove dangling images
docker image prune -a            # remove all unused images
docker system prune -a --volumes # remove EVERYTHING unused (aggressive)

.dockerignore

node_modules
.git
.env
dist
*.log

Without it, COPY . . drags junk into the image and breaks the cache. Deploying to a server from scratch - in the VPS article.