Lua

Prerequisite: This is Part 11 of the System Design Masterclass. Previous parts built the core components — this part covers securing APIs and managing client traffic spikes at scale. Answer-first: API rate limiting defends backend services by restricting request volume. Security requires a layered defense: Web Application Firewalls (WAF) block edge-level volumetric spikes, API Gateways manage L7 credentials and quotas, and application middleware enforces fine-grained business limits. Client identification must rely on validated, secure IP parsing (using the PROXY protocol or rightmost X-Forwarded-For checks). ...