Docker Complete Guide (A to Z)

🚀 What is Docker?

Docker is an open platform for developing, shipping, and running applications. It allows you to package applications and their dependencies into a container so they can run reliably in different computing environments.

• Containers are lightweight, fast, and portable compared to traditional Virtual Machines.

• Docker ensures your app works the same everywhere — from your laptop to production servers.

👉 Official Docs: Docker Overview

💻 Installation

🔹 Linux (Ubuntu/Debian)

sudo apt update
sudo apt install docker.io -y
sudo systemctl start docker
sudo systemctl enable docker
docker --version

🔹 Mac & Windows

• Install Docker Desktop 👉 Download Docker Desktop It comes with Docker Engine + Docker Compose + GUI.

🧰 Basic Docker Commands

👉 Docker Hub Images

🔑 Environment Variables in Containers

Environment variables are used to configure containers (e.g., DB credentials).

Example: Running MySQL with root password

docker run --name some-mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw -d mysql:8

👉 MySQL Docker Hub

📂 Docker Image Layers

• Docker images are built in layers.

• Each instruction in a Dockerfile creates a new read-only layer.

• Containers are writable layers on top of images.

Container Layer (Writable)
│
├─ Layer 2
├─ Layer 1
└─ Base Layer (Linux)

👉 Docker Image Concept

🔌 Port Binding

What is Port Binding?

Port binding connects a container’s internal port to a port on the host machine. This allows access to containerized apps from outside the container.

Syntax:

docker run -p <host_port>:<container_port> image

Example:

docker run -p 8080:80 nginx

• 8080 = host machine port

• 80 = container’s internal port

Access via: http://localhost:8080

👉 Docker Networking Basics

🛠️ Troubleshooting Commands

🆚 Docker vs Virtual Machine

🖥️ Docker Desktop

Docker Desktop is a GUI tool for Windows/Mac that includes:

• Docker Engine

• Docker CLI

• Docker Compose

• A simple GUI to manage containers, images, and volumes

👉 Docker Desktop Docs

🌐 Docker Networks

What is Docker Network?

A Docker network is a communication channel that allows containers to talk to each other or the outside world.

Types of Drivers

• bridge (default) → container-to-container on the same host

• host → shares host networking (faster, less isolation)

• null (none) → no networking

Commands

docker network ls                   # List networks
docker network create my_network    # Create custom network
docker run --network=my_network ... # Attach container to network

👉 Networking Docs

📦 Example: MongoDB + Mongo Express

1. Create a network:

docker network create mongo-network

2. Run MongoDB:

docker run -d --name mongodb \
  -e MONGO_INITDB_ROOT_USERNAME=admin \
  -e MONGO_INITDB_ROOT_PASSWORD=secret \
  --network mongo-network \
  mongo

3. Run Mongo Express:

docker run -d --name mongo-express \
  -e ME_CONFIG_MONGODB_ADMINUSERNAME=admin \
  -e ME_CONFIG_MONGODB_ADMINPASSWORD=secret \
  -p 8081:8081 \
  --network mongo-network \
  mongo-express

👉 Access UI: http://localhost:8081

📜 Docker Compose

What is Docker Compose?

Docker Compose is a tool for defining and running multi-container applications using a YAML file.

Example docker-compose.yaml

version: '3'
services:
  mongodb:
    image: mongo
    container_name: mongodb
    environment:
      - MONGO_INITDB_ROOT_USERNAME=admin
      - MONGO_INITDB_ROOT_PASSWORD=secret
    networks:
      - mongo-network

  mongo-express:
    image: mongo-express
    container_name: mongo-express
    ports:
      - '8081:8081'
    environment:
      - ME_CONFIG_MONGODB_ADMINUSERNAME=admin
      - ME_CONFIG_MONGODB_ADMINPASSWORD=secret
    networks:
      - mongo-network

networks:
  mongo-network:
    driver: bridge

Commands

docker compose -f docker-compose.yaml up -d
docker compose -f docker-compose.yaml down

👉 Compose Docs

📝 Dockerfile (Dockerizing Apps)

What is Dockerfile?

A Dockerfile is a script containing instructions to build a Docker image.

Example Dockerfile

FROM node:18          # Base image
WORKDIR /app          # Set working dir
COPY package*.json ./ # Copy files
RUN npm install       # Install deps
COPY . .              # Copy source code
EXPOSE 3000           # Expose port
CMD ["npm", "start"]  # Start app

Build & Run

docker build -t myapp:1.0 .
docker run -p 3000:3000 myapp:1.0

👉 Dockerfile Reference

📤 Push Image to Docker Hub

docker login
docker tag myapp:1.0 myusername/myapp:1.0
docker push myusername/myapp:1.0

👉 Publish to Docker Hub

💾 Docker Volumes (Persistent Data)

What is Docker Volume?

Volumes are persistent storage mechanisms in Docker that allow data to survive container restarts or deletion.

Types of Volumes

• Named Volume

  docker run -v mydata:/data ubuntu

Anonymous Volume

docker run -v /data ubuntu

Bind Mount

docker run -v /host/path:/container/path ubuntu

Manage Volumes

docker volume ls
docker volume create myvol
docker volume rm myvol
docker volume prune   # remove unused volumes

👉 Volumes Docs

📚 References

• 📘 Official Docs: Docker Docs

• 📺 YouTube Crash Course: Docker Tutorial

• 🐳 Docker Hub: hub.docker.com