Docker Cheat Sheet: Images, Containers, Compose & More

Quick reference tables

Images

Containers — run

Containers — manage

Containers — inspect & debug

Volumes

Networks

Docker Compose

Cleanup — reclaim disk space

Detailed sections

Writing a Dockerfile

# Start from a base image
FROM node:20-alpine

# Set working directory
WORKDIR /app

# Copy dependency files first (for layer caching)
COPY package*.json ./

# Install dependencies
RUN npm ci --omit=dev

# Copy application code
COPY . .

# Expose the port
EXPOSE 3000

# Set environment variable
ENV NODE_ENV=production

# Default command
CMD ["node", "server.js"]

Layer caching tip: Copy package.json and install dependencies before copying source code. Dependencies change less often than code — this way Docker only re-runs npm install when dependencies actually change.

Writing a docker-compose.yml

services:
  web:
    build: .
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production
      - DATABASE_URL=postgres://user:pass@db:5432/mydb
    volumes:
      - ./uploads:/app/uploads
    depends_on:
      - db
    restart: unless-stopped

  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: pass
      POSTGRES_DB: mydb
    volumes:
      - pgdata:/var/lib/postgresql/data
    restart: unless-stopped

volumes:
  pgdata:

Run it:

docker compose up -d
docker compose logs -f
docker compose exec web bash
docker compose down

Debugging a container that won’t start

# See what happened — check exit code and last logs
docker ps -a
docker logs <container_id>

# Try running with a shell instead of the default command
docker run -it --entrypoint bash myapp

# Or override the command
docker run -it myapp sh

# Inspect the full config
docker inspect <container_id>

Multi-stage builds — smaller production images

# Stage 1: Build
FROM node:20 AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# Stage 2: Production (no dev deps, no source)
FROM node:20-alpine
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/package*.json ./
RUN npm ci --omit=dev
EXPOSE 3000
CMD ["node", "dist/server.js"]

The final image only contains what the second stage copies — no build tools, no source code, no dev dependencies. Often 5–10x smaller.

.dockerignore — keep images clean

node_modules
.git
.env
*.log
dist
coverage
.DS_Store

Same syntax as .gitignore. Without this, COPY . . sends your entire project including node_modules to the build context, making builds slow and images bloated.

Useful one-liners

# Stop all running containers
docker stop $(docker ps -q)

# Remove all stopped containers
docker rm $(docker ps -aq)

# Get a container's IP address
docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' web

# Follow logs for all compose services
docker compose logs -f

# Rebuild and restart a single service
docker compose up -d --build web

# See environment variables inside a container
docker exec web env

# Export an image to a tar file
docker save myapp:v1 > myapp.tar

# Load an image from a tar file
docker load < myapp.tar

Want a real-world example? See How to Write a Production Dockerfile for Node.js.

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