A deeply-synthesized, opinionated reference distilled from five canonical sources: donnemartin/system-design-primer · ByteByteGoHq/system-design-101 · karanpratapsingh/system-design · ashishps1/awesome-system-design-resources · binhnguyennus/awesome-scalability Use it as: a study guide for interviews, a checklist for design reviews, and a vocabulary for cross-team discussions. Table of Contents 📖 How to Use This Playbook 🧠 The System Design Mindset 🔑 Core Mental Models 🎯 The Interview Framework (RAPID-S) 🔢 Back-of-Envelope Math 🌐 Networking Fundamentals 🌍 DNS, CDN, and Proxies ⚖️ Load Balancing & API Gateways 🗄️ Databases: Pick Your Engine 🔀 Replication, Sharding, Federation 🔒 Consistency, Transactions & Isolation ⚡ Caching 📨 Asynchronous Communication 🔌 API Design 🏗️ Architectural Patterns 🕸️ Distributed Systems Primitives 🛡️ Reliability & Resilience Patterns 📊 Observability, SLA/SLO/SLI 🔐 Security 📈 Capacity Planning & Scaling Playbook 🏭 Data Engineering & Analytics…