What is Docker?

Docker is an open-source platform that allows developers to package applications and their dependencies into lightweight, portable containers.

Containers ensure that applications run consistently regardless of where they are deployed.

The Problem Docker Solves

Before Docker, developers frequently encountered issues where an application worked perfectly on one machine but failed on another due to differences in:

• Operating systems
• Installed software
• Runtime versions
• Environment configurations

This led to the classic phrase:

"It works on my machine."

Docker solves this problem by packaging everything an application needs to run into a single, portable unit.

What Is a Container?

A container is an isolated environment that contains:

• Application code
• Runtime dependencies
• Libraries
• Configuration files
• System tools

Containers share the host operating system's kernel, making them lightweight and efficient.

Containers vs Virtual Machines

Containers	Virtual Machines
Lightweight	Heavyweight
Share host OS kernel	Include full guest OS
Fast startup	Slower startup
Lower resource usage	Higher resource usage

Docker Architecture

Docker consists of three primary components:

Docker Client

The Docker CLI used to interact with Docker.

docker run nginx

Docker Daemon

The background service responsible for:

• Building images
• Running containers
• Managing networks
• Managing volumes

Docker Registry

A storage location for Docker images.

Examples include:

• Docker Hub
• GitHub Container Registry
• Amazon Elastic Container Registry (ECR)

Benefits of Docker

Docker provides:

• Consistent environments
• Faster deployments
• Improved scalability
• Simplified onboarding
• Efficient resource utilization

Summary

Docker allows developers to package applications and dependencies into portable containers that can run consistently across different environments.