Your question is Appointment Data Pull at Scale. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You're building a system to sync appointments from 100k merchants (e.g., salons, doctors) so users can book online. Merchants expose GET /appointments?start_date=<>&end_date=<> (max 1 week per request, ~1 sec each). You must pull data for all merchants every 10 minutes. How would you design the data pull system to handle this scale?
Asked in the system design stage. 6 months of data = 26 requests/merchant. Reported follow-ups: How would you store the data (~1000 appointments/merchant) so that it's efficient to query free slots? What would you monitor and alert on?