Getting Started with Docker

What is Docker and Why Should You Care?

If you've ever heard "it works on my machine" — Docker is the cure. Docker lets you package applications with everything they need to run (code, runtime, libraries, config) into lightweight, portable containers.

Unlike virtual machines, containers share the host OS kernel, making them incredibly fast to start and efficient with resources.

Key Concepts

Images vs Containers

Think of a Docker image as a recipe and a container as the dish you cook from it:

• Image: A read-only template with instructions for creating a container
• Container: A running instance of an image — isolated, lightweight, and disposable

The Dockerfile

A Dockerfile is your recipe file. Here's a simple one for a Node.js app:

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

Each instruction creates a layer. Docker caches layers, so unchanged steps are blazing fast on rebuilds.

Essential Commands

• docker build -t myapp . — Build an image from a Dockerfile
• docker run -p 3000:3000 myapp — Run a container
• docker ps — List running containers
• docker stop — Stop a container
• docker compose up — Start multi-container apps

Real-World Workflow

1. Write your application code
2. Create a Dockerfile in your project root
3. Build the image: docker build -t myapp .
4. Test locally: docker run -p 3000:3000 myapp
5. Push to a registry: docker push myregistry/myapp
6. Deploy anywhere that runs Docker

What's Next?

Docker is the foundation of modern DevOps. Once you're comfortable with basics, explore:

• Docker Compose for multi-container applications
• Docker volumes for persistent data
• Multi-stage builds for smaller production images
• Container orchestration with Kubernetes

Ready to learn hands-on? Check out our Docker Fundamentals course — it includes interactive labs where you practice in real environments.