Design a CDN (Content Delivery Network) - System Design
A CDN sounds like a caching proxy you already know how to build: put an Nginx in front of the origin, set a TTL, done. That intuition …
Read MoreDesign a DNS Resolver System - System Design
A DNS resolver sounds like a lookup table: a client asks “what is the IP for example.com,” you return an A record, done. That intuition …
Read MoreDesign Jira (Bug / Issue Tracking) - System Design
Jira looks like a CRUD app with extra menus. Create a ticket, assign it, drag it across a board, close it. Say that in an interview and the …
Read MoreDesign Coursera / Online Learning Platform - System Design
An online learning platform looks like “YouTube with a login” for about a minute, and then the differences bite. Video is only one plane of …
Read MoreDesign Multiplayer Game Matchmaking - System Design
Everyone thinks matchmaking is “put waiting players in a list, grab the first ten, start a game.” That works in a hackathon demo with fifty …
Read MoreDesign Online Auction (eBay) - System Design
An online auction looks like “a listing with a current price that goes up,” and if you model it that way you will lose the interview in the …
Read MoreTechnical Debt Is a Business Problem - How to Get Your Manager to Care About Refactoring
Your manager does not care that the payment module is “a mess.” They have heard that sentence about six different modules from four …
Read MoreDesign Coinbase (Crypto Exchange) - System Design
“Let users buy and sell crypto” hides two different, both-irreversible problems welded together. Inside the exchange, Coinbase is a matching …
Read MoreDesign Robinhood (Stock Trading Platform) - System Design
“Let a user buy and sell stocks” sounds like a form that writes a row. Then you notice where the money and the shares actually live. …
Read MoreDesign Venmo / P2P Payment - System Design
Venmo looks like a wallet with a Twitter feed bolted on, and that framing is exactly what makes it interesting. The money side demands …
Read MoreNRI Investing in India - The NRE and NRO Account Confusion Finally Explained
Most NRIs I have talked to hold both an NRE and an NRO account, and almost none of them can tell you which money is supposed to go where. …
Read MoreDesign GitHub (Code Hosting + PRs) - System Design
“Host code and let people review changes” sounds like a CRUD app with a diff view. It is not. Under the hood you are running a fleet that …
Read MoreDesign LinkedIn (Professional Graph + Feed) - System Design
LinkedIn looks like Twitter with a suit on. It has a feed, it has profiles, people follow each other. So candidates walk in ready to reuse …
Read MoreDesign Tinder (Dating + Matching) - System Design
“Design Tinder” sounds like Instagram with a nicer gesture. Show a photo, swipe left or right, if two people both swipe right they can chat. …
Read MoreLLM Batch Inference Cuts API Costs in Half - When the Latency Trade-off Is Worth It
Most teams look at the 24-hour SLA on batch APIs and stop reading. That is a mistake. The word “batch” makes people picture overnight …
Read MoreDesign Reddit (Communities + Voting) - System Design
Reddit reads like three easy problems stapled together. Posts in communities: a table. Voting: a counter. Comments: a tree. Say it out loud …
Read MoreDesign Stack Overflow / Quora (Q&A) - System Design
Stack Overflow looks like a CRUD app. Post a question, others post answers, everyone votes, one answer gets accepted, and a number next to …
Read MoreDesign Zoom (Video Conferencing) - System Design
People hear “build Zoom” and reach for the WebRTC tutorial: two peers, an SDP exchange, media flows directly, done. That works for a 1:1 …
Read MoreState Machines Make AI Agents Predictable - Why Most Agent Designs Skip Them
Here is a claim that will annoy most people building agents right now: your agent does not have a bug, it has a state problem. The infinite …
Read MoreDesign Amazon Shopping Cart - System Design
A shopping cart sounds like a toy problem. “Store a list of item IDs and quantities for a user, let them add and remove, show it back.” You …
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