Docker lets you package your application with everything it needs (code, dependencies, system tools) into a single portable unit called a container.
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Installing Docker
Windows/Mac: Download Docker Desktop from docker.com
Linux:
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Your First Dockerfile
Let us containerize a simple Node.js app.
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Docker Compose Example
Let us run a Node.js app with a PostgreSQL database:
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Volumes: Persisting Data
By default, data inside containers is lost when the container stops. Volumes solve this.
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Best Practices
1. Use .dockerignore — exclude nodemodules, .git, .env files
2. Multi-stage builds — smaller production images
3. Use Alpine images — node:20-alpine is 50MB vs node:20 at 350MB
4. Do not run as root —
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When to Use Docker
- Development environments — consistent setup across team
- CI/CD pipelines — reproducible builds
- Microservices — each service in its own container
- Legacy apps — containerize old apps without chan
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When NOT to Use Docker
- Simple static websites (just use Vercel/Netlify)
- You are the only developer and the stack is simple
- Performance-critical applications where container overhead matters
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Learn Docker from scratch with this beginner-friendly guide. Covers containers, images, Dockerfile, docker-compose, volu