Design Migrate 1PB of Data to Cloud - System Design
“Move 1PB to the cloud” sounds like a copy job, and people design it like one: point a script at the source, rsync to an S3 bucket, wait. …
Read MoreDesign Slack (Team Messaging) - System Design
People hear “build Slack” and reach for a chat toy: a messages table, a WebSocket, insert on send, push to whoever is connected. That works …
Read MoreEmbedding Model Upgrades Silently Break Production RAG - Here Is How to Handle Them
A new embedding model drops, the benchmarks look great, and someone on your team changes one line of config to point at it. Nothing crashes. …
Read MoreDesign Ads Management & Display in Social Feed - System Design
Everyone models an ad server as a lookup: “the user opens the feed, we fetch an ad, we show it, done.” The interviewer lets that sit for a …
Read MoreDesign Distributed Document Editor (Notion / Wikipedia) - System Design
Almost everyone reaches for Google Docs the moment they hear “document editor,” and almost everyone is answering the wrong question. Google …
Read MoreDesign Toll Collection (FASTag) - System Design
A car drives through a toll lane at 30 km/h, an overhead antenna reads its RFID tag, and by the time the nose of the car reaches the barrier …
Read MoreIdempotency Keys Are How You Make Retries Safe in Distributed Systems
The network will lie to you. A client sends POST /charges, the server charges the card, and then the response is lost to a dropped …
Read MoreDatabase Connection Pooling Is the Performance Win Most Teams Skip
Most teams reach for a bigger database instance long before they reach for a connection pooler. That is backwards. A surprising amount of …
Read MoreDesign Flash Sale (6M Free Burgers in 1 Hour) - System Design
“Design a flash sale” sounds like a shopping-cart problem until you write down the actual numbers: Burger King runs a promo, the app has 50 …
Read MoreDesign IRCTC Train Booking (Tatkal) - System Design
“Book a train ticket” sounds like inserting a row. Then you look at Tatkal. At 10:00:00 sharp, a few days’ worth of demand for a scarce …
Read MoreDesign MakeMyTrip Travel Search - System Design
“Design MakeMyTrip” sounds like a shopping app: a user types two cities and a date, a list of flights comes back, they pick one and pay. The …
Read MoreDesign an Authentication & Login System - System Design
“Let users log in” is the request that hides an entire distributed system. You need to store a password without ever storing the password, …
Read MoreDesign Facebook Marketplace - System Design
Facebook Marketplace looks like “Craigslist with photos,” and if you design it that way you will fail the interview. The naive read is a …
Read MoreDesign Live Stock Prices Worldwide (Bloomberg) - System Design
“Show live prices for every stock on every exchange to millions of people at once” reads like a websocket that pushes a number. Then you …
Read MoreThe Outbox Pattern Is the Only Safe Way to Publish Events After a Database Write
The most dangerous line of code in a microservice is not the one that crashes. It is this one: order = db.save(order) # write to Postgres …
Read MoreDesign Cluster Health Monitoring - System Design
“Monitor the health of the cluster” sounds like a cron job that pings every box and pages someone when one goes quiet. Then you put 50,000 …
Read MoreDesign On-Call Escalation (PagerDuty) - System Design
Everyone thinks PagerDuty is a glorified SMS sender. “A monitoring tool posts an alert, you look up who is on call, and you text them. If …
Read MoreDesign P2P File Transfer (BitTorrent) - System Design
The whole point of a file-transfer service sounds like a solved problem: put the file on a server, hand out a URL, let people download. That …
Read MoreLong Context Windows Do Not Replace RAG - They Change When You Use It
Every few months someone declares RAG dead. The argument is always the same: context windows keep growing, so just stuff the whole corpus …
Read MoreClaude Code in a Team Setting - The Conventions Nobody Writes Down
One engineer using Claude Code is a productivity story. Ten engineers using Claude Code on the same repo, with no shared conventions, is a …
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