Problems / Resilience, medium
The database slows down. The API times out after 300 ms and retries 3 times with no backoff budget, tripling the load.
Free to open. Runs in your browser, no sign-up.
Success ≥ 99%, p99 ≤ 1 s.
1,500 requests a second for 30 seconds: 90% reads, 10% writes.
What each component does in this design, and what calls it. The simulator mimics each one from these settings.
| Component | Its job here | Settings |
|---|---|---|
| Load balancerLoad balancer | Traffic enters here.Calls API.Layer 4 balancers route by IP and port; layer 7 balancers read HTTP and can route by path or header. | – |
| APIApp service | Load balancer forwards to it.Calls Postgres.Little's law: throughput ≈ concurrency ÷ latency. 200 slots at 50 ms serve about 4,000 req/s. | 3 replicas × 200 slots · timeout 300 ms |
| PostgresSQL database | API calls it.Postgres runs one process per connection, which is why poolers like PgBouncer sit in front of busy databases. | 4 vCPU · 120 connections |
Try it first. Open one hint at a time if you get stuck.
Count calls into the database vs requests.
Retries into an overloaded service make it worse.
Limit retries (1, with a retry budget) and fix the timeout, then add capacity if needed.