Problems / Scaling, medium
Every read and write goes to one Postgres with 2 vCPUs, at 2,000 req/s. There is no cache.
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Success ≥ 99%, p99 ≤ 500 ms.
2,000 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 1.0 s |
| PostgresSQL database | API calls it.Postgres runs one process per connection, which is why poolers like PgBouncer sit in front of busy databases. | 2 vCPU · 80 connections |
Try it first. Open one hint at a time if you get stuck.
Which component crashes?
Most traffic is reads.
Read replicas share the reads; writes stay on the primary.
Add read replicas (or a cache) so the primary only takes writes and a share of reads.