Docker packages your application and its dependencies into a container that runs the same way everywhere — on your laptop, your teammate's laptop, and your production server.

Key concepts

• Image — a blueprint for a container (like a class in OOP)
• Container — a running instance of an image (like an object)
• Dockerfile — instructions for building an image
• docker-compose — tool for running multi-container apps

A minimal PHP Dockerfile

FROM php:8.2-apache
COPY . /var/www/html/
RUN docker-php-ext-install pdo pdo_mysql

docker-compose for a PHP + MySQL project

services:
  app:
    build: .
    ports:
      - "8080:80"
    volumes:
      - .:/var/www/html

  db:
    image: mysql:8
    environment:
      MYSQL_DATABASE: myapp
      MYSQL_ROOT_PASSWORD: secret

Run it with docker compose up and your entire stack starts in seconds.

Why bother?

• Onboarding a new developer takes minutes instead of hours
• No more version conflicts between projects
• Production environment matches development exactly

Once you start using Docker it is hard to go back.