Docker Images

A Docker image is a blueprint or template for a container. Think of it like a class in object-oriented programming or a recipe in cooking.

• Images are read-only templates
• They contain the application code, libraries, dependencies, tools, and other files
• Images can be shared via Docker Hub (a public registry) or private registries
• Common images include: nginx, php, mysql, wordpress

Docker Containers

A container is a running instance of an image. Think of it as an object instantiated from a class or a dish made from a recipe.

• Containers are isolated but can communicate with each other
• They are lightweight and start quickly
• Each container runs as a separate process
• Changes inside a container don't affect the image

Dockerfile

A Dockerfile is a text file with instructions for building a Docker image.

# Simple PHP Dockerfile example
FROM php:8.1-apache
COPY src/ /var/www/html/
RUN docker-php-ext-install mysqli pdo pdo_mysql
EXPOSE 80
CMD ["apache2-foreground"]

Docker Compose

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

# docker-compose.yml example
version: '3'
services:
  wordpress:
    image: wordpress:latest
    ports:
      - "8080:80"
    environment:
      WORDPRESS_DB_HOST: db
      WORDPRESS_DB_USER: wordpress
      WORDPRESS_DB_PASSWORD: wordpress
      WORDPRESS_DB_NAME: wordpress
    volumes:
      - ./wp-content:/var/www/html/wp-content
  
  db:
    image: mysql:5.7
    environment:
      MYSQL_ROOT_PASSWORD: rootpassword
      MYSQL_DATABASE: wordpress
      MYSQL_USER: wordpress
      MYSQL_PASSWORD: wordpress
    volumes:
      - db_data:/var/lib/mysql

volumes:
  db_data: