Free system design template
Capacity plan
Expected peak traffic, a sized design and Find my limit, with headroom and cost per month as criteria.
It opens with this template loaded and runs in your browser. You don't need an account to use it; a free account saves your work and exports it.
The job it does
Before a sale, a launch or the yearly budget: how much traffic can we take, and what does more cost? It comes with its own checks, so after you change it you can see at a glance that it still does the job.
What's inside
This is the template exactly as the System Design Studio opens it, read-only. Open it to run it, change it and export it.
- 7 parts
- Traffic 2,500 req/s, peak 6,000 req/s
- 90% reads, 10% writes
Before a sale, a launch or the yearly budget: how much traffic can we take, and what does more cost? Set the expected peak in the traffic profile, size each part (Inspector → size and replicas), and let the criteria hold you to the targets plus headroom.
This plan is for the festival sale: 2,500 requests a second normally, 6,000 at the peak, and the plan must hold 7,500 (25% headroom) under 250 ms at p95, for at most $3,000 a month. Press Find my limit to see the real ceiling and the cost per month, then try smaller instances or fewer replicas and compare.
- p95 latency ≤ 250 ms
- Error rate ≤ 1%
- Holds ≥ 7,500 req/s
- Costs ≤ $3,000/month
Parts
- Mobile app: Mobile app
- Web client: Web client
- Load balancer: Load balancer
- App server: App server, 10 replicas, Large (4 vCPU, 8 GB)
- Cache: Cache, 2 replicas, Medium (2 vCPU, 4 GB)
- DB read replica: DB read replica, 3 replicas, Medium (2 vCPU, 4 GB)
- DB primary: DB primary, 2 replicas, Large (4 vCPU, 8 GB)
Arrows
- Mobile app → Load balancer
- Web client → Load balancer
- Load balancer → App server
- App server → Cache
- App server → DB read replica
- App server → DB primary
- Peak 6,000 req/s × 1.25 headroom = 7,500 req/s to hold.; Users ≈ req/s × 10.
- Ask finance: is the monthly cost below inside the budget? What does +50% traffic cost?
The lesson behind it
Learn why it works, with a podcast and a quiz for each lesson.
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