Rate Limiting & Throttling (API Gateways).

Protecting backend services by limiting the number of requests a client can make in a specified time window.

API Gateways (Kong, AWS API Gateway) handle this using algorithms like Token Bucket or Leaky Bucket. Rate limiting protects against DDoS, prevents brute-force attacks, and allows monetization (e.g., Free Tier: 100 req/day). It stores state usually in an in-memory datastore like Redis.