API Request-Response Lifecycle

→ GET /api/v1/products/42 ← 200 OK {"id":42,"name":"Widget"}
Client App
Builds request
Method + URL + Headers + Body
→
←
API Gateway
Auth check
Rate limiting
Route request
→
←
Middleware
Logging
Auth verify
Input validation
→
←
App Logic
Business logic
Database query
Build response
2xx Success 4xx Client Error 5xx Server Error