How to Get Started with Docker for Beginners

What is Docker?

Docker is an open-source platform for automating the deployment, scaling, and management of applications using container technology. Containers package an application and its dependencies into a single, lightweight unit that can run consistently across different computing environments.

Key Docker Concepts

Installing Docker

Supported Platforms: Windows, macOS, Linux

Windows & macOS

1. Download Docker Desktop: https://www.docker.com/products/docker-desktop
2. Install the application following the prompts.
3. Start Docker Desktop and ensure it is running.

Linux (Ubuntu example)

sudo apt-get update
sudo apt-get install     ca-certificates     curl     gnupg
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
echo   "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/ubuntu   $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
sudo apt-get update
sudo apt-get install docker-ce docker-ce-cli containerd.io
sudo systemctl start docker
sudo systemctl enable docker

(Optional) Add your user to the docker group:

sudo usermod -aG docker $USER

Basic Docker Commands

Running Your First Container

Run a simple hello-world container:

docker run hello-world

Expected output: Docker downloads the image, runs it, and prints a hello message.

Working with Containers

1. Pull an Image
   sh
docker pull nginx
2. Run the Image
   sh
docker run -d -p 8080:80 --name webserver nginx
3. -d: Detached mode (runs in background)
4. -p 8080:80: Map host port 8080 to container port 80

5. --name webserver: Name the running container

6. Visit http://localhost:8080 in your browser to see the default Nginx page.

7. Stop and Remove the Container
   sh
docker stop webserver
docker rm webserver

Building Your Own Docker Image

1. Create a Simple Application

app.py:
python
print("Hello from Docker!")

1. Write a Dockerfile
   “`
   # Use official Python image
   FROM python:3.11-slim

# Set working directory
WORKDIR /app

# Copy source code
COPY app.py .

# Command to run
CMD [“python”, “app.py”]
“`

1. Build the Image
   sh
docker build -t my-python-app .

2. Run the Container
   sh
docker run my-python-app

Using Docker Compose

Docker Compose manages multi-container applications with a YAML file.

1. Example docker-compose.yml:
   yaml
version: "3"
services:
web:
image: nginx
ports:
- "8080:80"
redis:
image: redis:alpine

2. Start the Application
   sh
docker compose up -d

3. View Running Services
   sh
docker compose ps

4. Stop the Application
   sh
docker compose down

Data Persistence with Volumes

• Create a volume:
  sh
docker volume create mydata
• Use a volume with a container:
  sh
docker run -d -v mydata:/data busybox

Networking Basics

• List networks:
  sh
docker network ls
• Create a custom network:
  sh
docker network create mynet
• Run containers on the same network:
  sh
docker run -d --name db --network mynet postgres
docker run -d --name app --network mynet my-python-app

Best Practices

Troubleshooting Common Issues

Useful Resources

• Docker Documentation
• Docker Hub
• Play with Docker