HLD & LLD system design challenges – FAANG interview practice

Free, hands-on system design challenges covering HLD and LLD topics from junior SWE to staff level. Hold SLOs through traffic spikes, cache flushes and node failures on a live simulator. The closest thing to a real system design interview, in your browser, no signup.

• Hello, Load Balancer - One API server is drowning under 1,800 RPS. Get error rate to zero without touching the traffic.
• Cache Money - Your database is at 95% utilization serving reads it has answered a thousand times. Cool it down below 50%.
• The Stampede - Your cache will be flushed mid-run. Survive the stampede - keep errors under 5% while it refills.
• Queue It Up - Write traffic spikes 5× partway through. Absorb the burst without dropping a single write.
• Black Friday - Traffic is 12,000 RPS and the CFO capped infra at $1,400/hr. Keep p99 under 300ms and errors under 1%.
• Chaos Monkey - A monkey will kill one of your components mid-run. Design for redundancy so users never notice.
• The CTO Budget Cut - This system works - and burns $2,900/hr doing it. Hit the same SLOs for under $1,700/hr.