Scenario / The request path

Guided System Design Lesson: The Request Path

A small note-taking app needs the simplest real backend: one server and one database.

Run this scenario

Briefing

Request path fundamentals

One server and one database can serve a small app, and load percentages show how close each tier is to the edge.

One server and one database can serve a small app, and load percentages show how close each tier is to the edge.

One server and one database can serve a small app, and load percentages show how close each tier is to the edge.

  • Watch server load in the simulator.
  • Watch database load in the simulator.
  • Watch request path in the simulator.

Contract

Uptime

95%

P95 latency

600ms

Budget

$400/mo

Traffic shape

Daily traffic curve with a predictable high-traffic window. Baseline 90 users; peak around 470 users over 20 hours.

Available components

Server

HTTP request handler Every web app needs at least one server. More servers let you handle more simultaneous requests before latency starts climbing.

Postgres

Primary data store Without a database, your app has no memory. Most dynamic requests eventually depend on it.

Common mistakes

  • Adding capacity after the bottleneck has already saturated.

Interview adjacency

  • Explain request-response flow
  • Design a simple web app
  • Identify server and database load