The CTO Budget Cut – cto-level system design challenge

This system works - and burns about $15,000/month doing it. Hit the same SLOs for under $1,500/month.

Requirements

• Traffic: 4,000 req/s
• p99 latency: ≤ 250 ms
• Errors: ≤ 0.5%
• Budget: ≤ $1,500/month

Goal

Hold p99 latency under 250ms, error rate under 0.5%, cost under $1,500/month through every stage of the test plan, then compare your design with a reference design.

The test plan

1. A normal week: 4,000 requests per second.

Hint

Over-provisioning hides everywhere: anything under 30% utilization is money on fire. And find the biggest line on the bill - a service billed per request can cost more than every server combined.

Solve it on the live simulator, free and in your browser.

More system design challenges

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• Queue It Up - Write traffic spikes 5× partway through. Absorb the burst without dropping a single write.
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• Design a Chat System - Messages and history reads grow to 10,000 a second, then New Year's midnight triples it. Keep sends fast and every message delivered within 10 seconds, within budget.
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• Black Friday - Traffic is 12,000 RPS and the CFO capped infra at $3,000/month. Keep p99 under 300ms and errors under 1%.
• Chaos Monkey - A monkey will kill your busiest API server mid-run. Design for redundancy so users never notice.