System Design
From caching to designing Twitter — learn how real-world systems are built, step by step.
Fundamentals
Building Blocks
CAP Theorem
You can't have it all — pick two out of three→
Consistent Hashing
Adding a server shouldn't reshuffle everything→
Message Queues
Don't do everything right now — put it in line→
API Design
The contract between your system and the world→
Content Delivery Networks
Serve content from the closest shelf, not the warehouse→
Web Services
Social & Communication
Design a Chat System
Real-time messaging for millions — delivered instantly→
Design a Notification System
The right message, to the right person, at the right time→
Design a News Feed
Delivering personalized content to millions — instantly→
Design an Image Hosting Service
Upload, store, and serve images at scale — like Imgur→
Design a Video Streaming Service
Upload, transcode, and stream video to millions — like YouTube→
Design a Social Network
Connect billions of people — profiles, friends, and feeds at scale→
Design a Collaborative Editor
Multiple cursors, one document — real-time editing at scale→
Design a Music Streaming Service
Stream 100M+ songs to millions of listeners — like Spotify→
Data & Infrastructure
Design a Key-Value Store
Build a distributed hash map like Redis or DynamoDB — at planet scale→
Design a File Storage System
Upload, sync, and share files across every device — like Dropbox→
Design a Task Queue
Distribute background jobs reliably — like Celery and SQS→
Design a Web Crawler
Crawl the entire web like Googlebot — politely and at scale→
Design a Search Engine
Index billions of pages and return relevant results in milliseconds→
Design an Object Storage
Store unlimited objects with 11 nines of durability — like AWS S3→
Design a Metrics Monitoring System
Collect, store, query, and alert on millions of time-series data points — like Datadog and Prometheus→
Business Systems
Design a Payment System
Move money safely, exactly once, every time→
Design a Ride Sharing Service
Match riders with nearby drivers in real-time — at massive scale→
Design an E-Commerce Platform
Build Amazon-scale shopping — from catalog to checkout to delivery→
Design a Food Delivery System
Connect hungry customers with restaurants and delivery drivers — at scale→
Design a Ticket Booking System
Sell out stadiums without selling a seat twice→
Design an Ad Click Aggregator
Count billions of ad clicks accurately — for billing and analytics→