Efficiency

Essentials gets a production incident diagnosed. Efficiency is for designing the thing so it doesn't page you at 2am in the first place — the front door your API sits behind, the browser rule that trips up every back-end dev, and certificate renewal that never expires unattended again.

• HTTP

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  What Is CORS? — why the browser blocks cross-origin calls, and how the server actually grants permission.

• API Gateways

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  Reverse Proxy vs API Gateway — how production APIs handle TLS, routing, auth, and rate limiting before traffic ever reaches your code.

• TLS

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  ACME Protocol Explained — how HTTP-01 and DNS-01 challenges prove domain ownership, and the automation that renews certificates forever.

More Efficiency topics — VPC design, Kubernetes networking (Services, Ingress, Network Policies), and CDN basics — are still on the way.

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Start with What Is CORS? — the browser behavior that confuses more back-end engineers than anything else in this tier.