What is Docker? (Simple Definition)

Why Do Developers Use Docker?

Without Docker: "It works on my machine, not on the server!”

With Docker: "The environment is the same everywhere — no more config issues or “missing dependency” errors."

Real-Life Analogy

Imagine you’re a chef preparing a dish in your kitchen. You want to ship your recipe to another chef far away.

Without Docker:

• You give them ingredients and instructions. But their kitchen may not have the same tools, so the dish may fail.

With Docker:

• You ship the whole ready-made kitchen with ingredients, tools, and instructions. They just plug it in and cook.

What is a Docker Container?

A container is a lightweight, standalone, and executable package that includes:

• App code

• Libraries

• Runtime (e.g., Node, PHP)

• Configuration

It runs isolated from the host machine — so it doesn’t mess with your system settings.

What is a Docker Image?

A Docker Image is a blueprint.
You create an image with a Dockerfile, and Docker uses that image to launch containers.

Think of it as:

• Image = Class (Definition)

• Container = Object (Instance)

🧾 Example:

Run a Laravel application in Docker with MySQL as the database — all containerized

Step 1: Create Dockerfile (Laravel App)

This file tells Docker how to build your Laravel app image.

# Dockerfile

FROM php:8.2-fpm

# Install dependencies

RUN apt-get update && apt-get install -y \

build-essential \

libpng-dev \

libjpeg62-turbo-dev \

libfreetype6-dev \

locales \

zip \

jpegoptim optipng pngquant gifsicle \

vim unzip git curl \

libonig-dev \

libxml2-dev \

libzip-dev

# Install PHP extensions

RUN docker-php-ext-install pdo pdo_mysql mbstring exif pcntl bcmath gd zip

# Install Composer

COPY --from=composer:latest /usr/bin/composer /usr/bin/composer

# Set working directory

WORKDIR /var/www

COPY . .

RUN composer install

CMD ["php-fpm"]

EXPOSE 9000

Step 2: Create docker-compose.yml

This file defines and runs multi-container Docker apps — here: Laravel (PHP), MySQL, Nginx.

version: '3.8'

services:

app:

build:

context: .

dockerfile: Dockerfile

image: laravel-app

container_name: laravel-app

restart: unless-stopped

working_dir: /var/www

volumes:

- ./:/var/www

networks:

- laravel

db:

image: mysql:8.0

container_name: mysql-db

restart: unless-stopped

environment:

MYSQL_ROOT_PASSWORD: root

MYSQL_DATABASE: laravel

MYSQL_USER: user

MYSQL_PASSWORD: password

ports:

- "3306:3306"

volumes:

- db_data:/var/lib/mysql

networks:

- laravel

nginx:

image: nginx:alpine

container_name: nginx-server

restart: unless-stopped

ports:

- "8000:80"

volumes:

- ./:/var/www

- ./nginx.conf:/etc/nginx/conf.d/default.conf

depends_on:

- app

networks:

- laravel

volumes:

db_data:

networks:

laravel:

driver: bridge

Step 3: Create nginx.conf

# nginx.conf

server {

listen 80;

index index.php index.html;

server_name localhost;

root /var/www/public;

location / {

try_files $uri $uri/ /index.php?$query_string;

}

location ~ \.php$ {

fastcgi_pass app:9000;

fastcgi_index index.php;

include fastcgi_params;

fastcgi_param SCRIPT_FILENAME $realpath_root$fastcgi_script_name;

fastcgi_param DOCUMENT_ROOT $realpath_root;

}

location ~ /\.ht {

deny all;

}

}

Step 4: Update Laravel .env File

DB_CONNECTION=mysql

DB_HOST=db

DB_PORT=3306

DB_DATABASE=laravel

DB_USERNAME=user

DB_PASSWORD=password

Step 5: Start Docker

In your project folder, run: docker-compose up -d

• Then run the Laravel setup:

docker exec -it laravel-app php artisan migrate

docker exec -it laravel-app php artisan key:generate

Visit the app in browser:
👉 http://localhost:8000

✅ What You Just Did

You now have:

• A Laravel container running PHP + Composer

• A MySQL container with persistent storage

• Nginx as a web server routing traffic to Laravel

• Isolated, portable setup that works across any machine

🧩 Why This is Awesome

• No need to install PHP/MySQL on your system

• Same environment in dev, staging, or production

• Easily sharable and deployable (on AWS, EC2, etc.)