Payment Service

Endpoint

POST /pay

{ "userId": 1, "amount": 10, "requestId": "abc-123" }

Symptoms

• Duplicate charges
• 200 OK but no DB record
• Instability under load

Setup

bun i
bun run db:init
bun run dev

Load test

bun run load

Architecture

src/
├── server.js      # Express server on :3000
├── payRoute.js    # Payment endpoint
└── db.js          # SQLite helpers

• SQLite database in db/app.sqlite
• External payment provider (AWS Lambda, no local setup needed)