Docker Tutorial – Complete Beginner to Advanced Guide

Introduction to Docker

What is Docker?

Docker is an open-source containerization platform that simplifies building, shipping, and running applications across environments. It packages applications and their dependencies into containers, making them portable and consistent.

Why Use Docker?

“It works on my machine” is no longer an excuse.

Docker ensures consistent environments across development, testing, and production. It reduces bugs caused by environmental differences.

Key Concepts in Docker

• Image – Blueprint for containers
• Container – Running instance of an image
• Dockerfile – Script to automate image creation
• Docker Hub – Cloud registry for sharing images

Getting Started with Docker

Prerequisites

• Basic command-line knowledge
• Familiarity with Linux
• Admin rights on your system

Installing Docker

Docker Desktop (Windows/macOS)

• Download from docker.com
• Run the installer and complete setup
• Verify with: docker --version

Docker Engine (Linux)

sudo apt update
sudo apt install docker-ce docker-ce-cli containerd.io

Docker Architecture

• Docker Daemon: Runs as a background service
• Docker Client: CLI tool to interact with Docker
• Registries: Repositories like Docker Hub that store images

Core Docker Components

Docker Images

What is an Image?

An image is a read-only template that defines the environment your app will run in.

Building Docker Images

FROM node:18
WORKDIR /app
COPY . .
RUN npm install
CMD ["node", "app.js"]

Build the image:

docker build -t my-node-app .

Docker Containers

Creating and Running Containers

docker run -d -p 3000:3000 my-node-app

Stopping and Removing Containers

docker ps
docker stop <container_id>
docker rm <container_id>

Dockerfile Basics

Writing a Dockerfile

• FROM – Base image
• COPY – Copy project files
• RUN – Execute shell commands
• CMD – Set container start command

Best Practices

• Use .dockerignore
• Minimize image layers
• Pin exact versions

Docker Commands Cheat Sheet

Image Commands

docker images
docker rmi <image_id>

Container Commands

docker ps
docker logs <id>
docker exec -it <id> bash

Network & Volume Commands

docker network ls
docker volume ls

Docker Compose

What is Docker Compose?

A tool to define and manage multi-container Docker applications using a docker-compose.yml file.

Installing Docker Compose

Docker Desktop includes Compose. On Linux:

sudo apt install docker-compose

Sample docker-compose.yml

version: "3"
services:
  web:
    build: .
    ports:
      - "5000:5000"
  redis:
    image: redis:alpine

Run with Compose

docker-compose up

Working with Docker Hub

Pull Images

docker pull nginx

Push Images

docker tag my-app username/my-app
docker push username/my-app

Real-World Use Cases

Docker in Development

Quick setup of dev environments. No more dependency hell.

Docker in CI/CD Pipelines

Jenkins, GitHub Actions, and GitLab CI use Docker to ensure reliable builds/tests.

Production Deployment

Use orchestration tools like Kubernetes or Docker Swarm for high availability and scaling.

Best Practices for Docker

• Use smaller base images (e.g., Alpine)
• .dockerignore to exclude unnecessary files
• Tag images properly (e.g., myapp:1.0)

Common Docker Issues and Fixes

Container Not Starting

docker logs <container_id>

Port Conflicts

Ensure no other app is using the specified port.

Permission Issues

Use sudo or add your user to the Docker group:

sudo usermod -aG docker $USER

Security in Docker

Docker Security Basics

• Avoid running as root inside containers
• Update base images frequently

Run with Least Privileges

docker run --user 1000:1000 ...

Avoid --privileged unless absolutely necessary.

Docker Ecosystem and Alternatives

Podman vs Docker

Podman is rootless and daemonless — a good alternative in secure environments.

Kubernetes & Docker

Kubernetes can orchestrate Docker containers. However, recent versions support runtimes like containerd and CRI-O.

Conclusion

Docker revolutionizes how we develop, test, and deploy software. It’s portable, fast, and scalable—ideal for both personal and enterprise projects. Master Docker to future-proof your development workflow.