Docker: From Beginner to Pro

Introduction to Docker

Docker is a powerful platform that enables developers to build, deploy, and run applications in lightweight, portable containers. Unlike traditional virtual machines, Docker containers share the host OS kernel, making them faster and more efficient.

Why Use Docker?

•  Consistency: Works the same across different environments (development, testing, production).

•  Isolation: Applications run in separate containers, avoiding dependency conflicts.

•  Portability: Easily move containers between systems.

•  Scalability: Quickly scale applications using container orchestration tools like Kubernetes.

Docker Basics for Beginners

1. Key Docker Concepts

• Container: A lightweight, standalone executable package that includes everything needed to run an application.

• Image: A read-only template used to create containers (e.g., nginx, ubuntu).

• Dockerfile: A script that defines how to build a Docker image.

• Docker Hub: A public registry to share and pull Docker images.

2. Installing Docker

• Linux:

sudo apt-get update && sudo apt-get install docker.io

• Windows/macOS: Download Docker Desktop from Docker’s official website.

3. Basic Docker Commands

# Pull an image from Docker Hub 

docker pull nginx 

# Run a container 

docker run -d -p 8080:80 --name my-nginx nginx 

# List running containers 

docker ps 

# Stop a container  

docker stop my-nginx 

# Remove a container 

docker rm my-nginx 

Intermediate Docker: Custom Images & Docker Compose

1. Creating a Custom Docker Image

Example Dockerfile:

FROM python:3.8-slim 

WORKDIR /app 

COPY . . 

RUN pip install -r requirements.txt 

CMD ["python", "app.py"] 

Build and run:

docker build -t my-python-app . 

docker run -d -p 5000:5000 my-python-app 

2. Managing Multiple Containers with Docker Compose

Example docker-compose.yml:

version: '3' 

services: 

  web: 

image: nginx 

ports: 

   - "8080:80" 

  db: 

image: mysql 

environment: 

   MYSQL_ROOT_PASSWORD: example 

Run with:

docker-compose up -d 

Advanced Docker for Professionals

1. Docker Networking

• Bridge Network (Default): Isolated containers on a single host.

• Host Network: Shares the host’s network stack.

• Overlay Network: Connects containers across multiple hosts (used in Swarm/Kubernetes).

2. Docker Security Best Practices

• Use minimal base images (e.g., alpine instead of ubuntu).

• Run containers as non-root users:

USER nobody 

• Scan images for vulnerabilities:

   docker scan <image-name> 

3. Docker in CI/CD Pipelines

Example GitHub Actions workflow:

jobs: 

  build-and-push: 

runs-on: ubuntu-latest 

steps: 

   - uses: actions/checkout@v2 

   - run: docker build -t my-app . 

   - run: docker login -u ${{ secrets.DOCKER_USER }} -p ${{ secrets.DOCKER_PASS }} 

   - run: docker push my-app 

4. Kubernetes & Docker Swarm for Orchestration

•  Kubernetes: Manages large-scale container deployments.

•  Docker Swarm: Simpler alternative for smaller clusters.

Real-World Docker Use Cases

1. Microservices Architecture

• Each service runs in its own container, enabling independent scaling.

2. DevOps & Continuous Deployment

• Docker ensures consistency between development and production.

3. Legacy Application Modernization

• Run old applications in containers without full VM overhead.

4. Data Science & Machine Learning

• Reproducible environments for training models.