Problems / Scaling, hard
The prototype goes live as it is: one API replica with 2 vCPUs, a 2-vCPU database with a 40-connection pool, and no cache, at 2,500 requests a second.
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Success ≥ 99%, p99 ≤ 500 ms.
2,500 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. | 1 replicas × 150 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 · 40 connections |
Try it first. Open one hint at a time if you get stuck.
More than one component turns red: fix the first one on the request path, rerun, then look again.
The API needs slots and CPU for 2,500 req/s; the database needs reads taken off it.
Replicas for the API; read replicas or a cache for the database.
Scale the API to 5 or more replicas, then give the database read replicas (or put a cache in front of it).