Clean canvas, 45-minute timer, optional hints, and a scored report. Prompt list is free to browse; timed sessions need Pro.
Warm up with the capacity drill or the 6-month roadmap.
Build the system that powers a service like bit.ly. Reads should be very fast; writes are rare. Plan for 100M URLs created, 10B redirects per month.
When a user opens the app, they see a personalized feed. New posts should appear in followers' feeds within seconds (for typical users). Plan for 1B users.
Real-time 1:1 and group messaging. Messages must be delivered with sub-second latency to online users, and reliably to offline users. Plan for 2B users globally.
On a ride request, find the nearest available driver in < 2s. Drivers stream their GPS location every few seconds. Plan for 5M concurrent drivers at peak.