Docker 101

1. Introduction to Docker One of the biggest historical challenges in software engineering has been environment inconsistency , the frustrating situation where an application works perfectly on one machine but unexpectedly fails elsewhere. And this is precisely the problem Docker was designed to solve. Docker is a containerization platform that packages applications and their dependencies into isolated environments called containers . Its goal is simple: Run applications consistently everywhere. Instead of configuring every machine manually, Docker packages everything an application needs to run. 1.1 What is Docker? Docker is a platform used to build, package, and run applications inside containers. A container includes: Application code Dependencies Runtime Libraries Configuration Simple mental model: Code + Dependencies + Runtime = Container This ensures applications behave the same way across development, testing, and production environments. 1.2 VMs vs Containers VMs (Virtual Machines) package: Application Dependencies Full Operating System Containers package only: Application Dependencies Runtime Containers share the host operating system kernel, making them much lighter and faster. Feature Virtual Machine Docker Container Includes OS Yes No Startup Speed Slow Fast Resource Usage Heavy Lightweight Size Large Small Simple analogy: Virtual Machine = Full House Container = Apartment in a Building 1.3 Docker Ecosystem Overview Docker includes multiple tools: Docker Engine The core service that runs containers. Docker Desktop A local GUI and development environment. Docker Hub A cloud registry for storing and sharing Docker images. Docker Compose A tool for running multiple containers together. Example: docker compose up Can start an entire application stack: Backend API Database Redis Frontend with a single command. 2. Docker Architecture & Fundamentals To use Docker effectively, it is important to understand how its core components work together. Docker follows a