Can you explain what Docker is and how it is used for containerizing applications?

Docker is a platform for containerizing applications that allows you to package a program along with all its dependencies into an isolated container. Containers provide a consistent runtime environment on any server where Docker is installed.

Main advantages of Docker:

• Portability — containers run the same way in different environments (local, test, production).
• Isolation — applications and their dependencies do not conflict with each other.
• Lightweight — containers use resources more efficiently than virtual machines.

In practice, Docker is used for:

• Rapid deployment of applications.
• Environment version management.
• Automation of CI/CD processes.

Example Dockerfile for a PHP application:

FROM php:8.1-apache
COPY src/ /var/www/html/
RUN docker-php-ext-install mysqli pdo pdo_mysql

This file describes an image that contains PHP with Apache and copies the application's source code into the container.