Chapter 6: HTTP, REST APIs, and API Gateway Patterns

HTTP Methods (Verbs)

REST API Design

// Resources as nouns, HTTP verbs as actions:
GET    /users          → list users
GET    /users/123      → get user 123
POST   /users          → create user
PUT    /users/123      → replace user 123
PATCH  /users/123      → update fields of user 123
DELETE /users/123      → delete user 123
GET    /users/123/orders → list orders for user 123

API Gateway Pattern

Idempotency

An operation is idempotent if calling it multiple times produces the same result as calling it once. Critical for retries in distributed systems.

// Idempotent: safe to retry
GET /users/123           → always returns same user
PUT /users/123 {name:"Bob"} → always sets name to Bob
DELETE /users/123        → user is deleted (already deleted = still deleted)

// NOT idempotent: dangerous to retry
POST /orders {item:"book"} → creates a NEW order each time!
// Fix: use idempotency key
POST /orders {item:"book", idempotency_key:"abc123"}
// Server checks: already processed abc123? Return cached response.

HTTP Status Codes