Docker

TL;DR

One-liner: Docker packages apps into containers that run identically everywhere - no more “works on my machine” problems.

Core Value:

• Consistent environments - same setup from dev to production
• Isolation - apps don’t interfere with each other
• Portability - runs on any machine with Docker installed
• Lightweight - shares host OS kernel, not a full VM

Quick Start

Install

macOS/Windows: Download Docker Desktop

Linux:

curl -fsSL https://get.docker.com | sh
sudo usermod -aG docker $USER
# Logout and login again

Verify

docker --version

First Container

docker run hello-world

Run a Web Server

docker run -d -p 8080:80 nginx
# Open http://localhost:8080

Cheatsheet

Command	Description
docker run IMAGE	Run a container
docker run -d IMAGE	Run in background
docker run -p 8080:80 IMAGE	Map port
docker run -v /host:/container IMAGE	Mount volume
docker ps	List running containers
docker ps -a	List all containers
docker images	List images
docker pull IMAGE	Download an image
docker stop ID	Stop a container
docker rm ID	Remove a container
docker rmi IMAGE	Remove an image
docker logs ID	View container logs
docker exec -it ID bash	Shell into container

Gotchas

Permission denied on Linux

sudo usermod -aG docker $USER
# Then logout and login again

Port already in use

# Use a different host port
docker run -p 3001:80 nginx

Container stops immediately

# Run interactively to debug
docker run -it IMAGE bash

# Check logs
docker logs CONTAINER_ID

Dockerfile not updating

# Build without cache
docker build --no-cache -t myapp .

Volume permissions

# Run as current user
docker run -u $(id -u):$(id -g) -v $(pwd):/app IMAGE

Next Steps

• Dockerfile Reference
• Docker Compose
• Docker Hub
• Docker Best Practices