What is Docker?

Docker packages your app and all its dependencies into a **container** — a lightweight, portable environment that runs the same everywhere.

No more "it works on my machine."

Core Concepts

• **Image**: A blueprint for your container (like a class)
• **Container**: A running instance of an image (like an object)
• **Dockerfile**: Instructions to build an image
• **Volume**: Persistent storage for containers
• **docker-compose**: Run multiple containers together

Your First Dockerfile

```dockerfile FROM node:20-alpine WORKDIR /app COPY package*.json ./ RUN npm install COPY . . EXPOSE 3000 CMD ["npm", "start"] ```

Running It

```bash docker build -t my-app . docker run -p 3000:3000 my-app ```

That's it. Your app is containerized. Visit localhost:3000.

Why Students Should Care

• Deploy projects easily for demos
• No "install X, Y, Z" for teammates
• Learn a skill every company wants