The pages I wanted when I was preparing
If you have to explain a design tomorrow, write a Go solution you can defend, or scrub a log before you paste it — this is the tab I wanted open. I write each page the way I would teach a colleague.
Featured walkthroughs
Taught from the failure first. Two riders, one driver. A tweet to thirty million people.
Pick a product you already use.
Start here
Interview framework
Estimation, storage, caching, messaging, and how to structure the hour.
Drill listQuestion bank
High-frequency HLD and LLD questions, each with a 60-second answer.
Product walkthroughs
Twitter
Hybrid fan-out: push ordinary authors, pull celebrities.
Uber
GEO finds candidates. A CAS assigns exactly one driver.
YouTube
Presigned upload, async ABR, then CDN playback — not an UPDATE on the video row.
Netflix
Licensed catalog, Open Connect-style CDN, licenses, and watch resume.
Instagram
Photos never enter the API. Home is a list of ids. Stories last 24 hours.
Rate limiter
Token bucket in Redis, the fixed-window burst bug, and fail-open vs fail-closed.
Outbox
You cannot commit Postgres and Kafka in one step. Same-transaction outbox, then a worker.
Parking lot
LLD. Two gates, one stall. The ticket plus an atomic occupy is the lock.