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the production readiness review
Every challenge ends in a Production Readiness Review: your design runs against real traffic and injected failures. The grade reflects what actually happened in the sim — not keywords in your justification.
Design a URL shortener serving 5,000 redirects/sec with a 100:1 read/write ratio. Survive a viral-link traffic spike and a primary database crash — on a $3,500/month budget.
Traffic
5k rps
3× spike
Budget
$3.5k
/mo
Est. time
60m
5 phases
You're on call. The flash sale started 10 minutes ago and checkout error rates are climbing past 50%. You inherit the system as it runs — diagnose the bottleneck, fix the architecture under a $2,000/month budget, and be ready for the next sale and a region outage.
Traffic
4k rps
2× spike
Budget
$2k
/mo
Est. time
60m
5 phases
An 8-second network hiccup that failed 30% of payment requests turned into a 45-minute outage because clients retried immediately with no backoff, multiplying load by 4x. Diagnose the retry amplification cascade, fix the retry logic with exponential backoff and jitter, add a circuit breaker on payment-db, and propose system-level defenses that prevent this failure mode from being possible.
Traffic
2k rps
4× spike
Budget
$1.5k
/mo
Est. time
45m
4 phases
A seed-funded photo feed app just raised its Series A. Your job is to design a system that works at 2,000 rps today, survives a 5x growth to 10,000 rps after the press cycle, and is architecturally ready for the 40,000 rps a Series B brings -- all within per-stage infrastructure budgets. 90% of traffic is feed reads. The personalization requirement changes everything about what you can cache.
Traffic
2k rps
3× spike
Budget
$8k
/mo
Est. time
75m
5 phases
Design a real-time chat system supporting 100k concurrent WebSocket connections, channel fan-out to 1,000 members, message history, and TTL-based presence — all within a $5,000/month budget. The hard problems are cross-gateway fan-out (a message sent to gateway-1 must reach users on gateway-2) and surviving a gateway crash without losing messages in flight.
Traffic
5k rps
3× spike
Budget
$5k
/mo
Est. time
60m
5 phases