/ Lab · Interactive
System Design Simulator
Every architecture works on a whiteboard. Build one here, send it real traffic, and watch where it breaks. Then fix it without blowing the budget.
A post took off. Keep up with 2,000 requests/second on a startup budget.
Hold every goal for 30 seconds straight. Changing the design restarts the clock.
- p95 ≤ 150 ms…
- errors ≤ 1.0%…
- cost ≤ $500/mo…
Live · t = 0s
Scroll sideways to see the whole system →
Traffic in
–
p95 latency
–
Error rate
–
Monthly cost
–
Last 60s. Dashed line = challenge goal. Hover a chart for exact values.
›How the model works
Each tier has a capacity in requests per second. Latency grows with utilization the way a single queue does (base time ÷ (1 − utilization)), so a tier at 90% is ten times slower than an idle one. Anything beyond 100% is rejected and counts as errors.
A CDN serves the 40% of requests that are static files. A cache answers the chosen share of reads. Replicas split reads with the primary database, but every write lands on the primary. A queue accepts writes instantly and drains them into the database's spare capacity.
Autoscaling adds one server every 3 seconds when servers pass 60% busy and removes them slowly, so it lags behind sudden spikes, just like the real thing.
Prices are rounded, illustrative on-demand list prices per month. The model is deliberately simple: the point is the trade-offs, not a quote. Read the engine.