Docker for Developers Who Keep Putting It Off

Docker's documentation starts with the big picture — images, registries, orchestration, Kubernetes. Most developers need to containerize a specific app for local development or deployment, not learn container theory. Start here.

A Dockerfile That Actually Works for a Node App

FROM node:20-alpine

WORKDIR /app

# Copy and install dependencies first (Docker layer caching)
COPY package*.json ./
RUN npm ci

# Copy source code
COPY . .

# Build if needed
RUN npm run build

# Expose port and start
EXPOSE 3000
CMD ["node", "dist/index.js"]

The order matters: copy package.json and install before copying source code. Docker caches each layer — if only your source code changed (not dependencies), Docker reuses the cached dependency layer, making rebuilds significantly faster.

The Commands You'll Use 90% of the Time

• docker build -t myapp . — build an image from the Dockerfile in the current directory, tag it 'myapp'.
• docker run -p 3000:3000 myapp — run the container, map port 3000 in the container to port 3000 on your host.
• docker run -d --name myapp -p 3000:3000 myapp — detached mode (background), with a name.
• docker ps — list running containers. docker ps -a shows stopped containers too.
• docker logs myapp -f — follow logs from a container. Essential for debugging.
• docker exec -it myapp sh — get a shell inside a running container. Use bash if sh doesn't work.
• docker stop myapp && docker rm myapp — stop and remove a container.
• docker images — list local images. docker rmi myapp — delete an image.

Docker Compose for Local Development

version: '3.8'
services:
  api:
    build: .
    ports:
      - '3000:3000'
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432/myapp
    depends_on:
      - db
  db:
    image: postgres:16-alpine
    environment:
      - POSTGRES_USER=user
      - POSTGRES_PASSWORD=pass
      - POSTGRES_DB=myapp
    volumes:
      - postgres_data:/var/lib/postgresql/data
volumes:
  postgres_data:

docker-compose up starts both. The db hostname resolves to the postgres container automatically. The volume postgres_data persists database data between restarts. docker-compose down stops everything. docker-compose down -v also deletes the volumes (destroys the database).

The .dockerignore File You're Forgetting

Without it, COPY . . copies your node_modules (500MB+), .git directory, .env files, and everything else into the image. Create .dockerignore:

node_modules
.git
.env
*.log
dist
.next