Docker Tutorial

Docker packages your app and its dependencies into a portable image that runs the same everywhere.

A minimal Dockerfile

FROM node:20-alpine
WORKDIR /app
COPY package*.json ./
RUN npm ci --omit=dev
COPY . .
EXPOSE 3000
CMD ["node", "server.js"]

Build and run:

docker build -t myapp .
docker run -p 3000:3000 myapp

Layers and caching

Order your Dockerfile so the least-changing steps come first. COPY package*.json + npm ci before copying source means code changes don’t invalidate the dependency layer.

Persistent data with volumes

docker volume create appdata
docker run -v appdata:/data myapp

Multi-container with compose

# docker-compose.yml
services:
  web:
    build: .
    ports: ["3000:3000"]
  db:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: secret
    volumes:
      - pgdata:/var/lib/postgresql/data
volumes:
  pgdata:

Run everything with docker compose up.

Keep images small: prefer -alpine bases and multi-stage builds for compiled languages.