...The material covers topics such as scaling from zero to millions of users, back-of-the-envelope estimation, rate limiters, consistent hashing, key-value stores, unique ID generators, URL shorteners, and web crawlers. It is intended as a work-in-progress reference rather than a full original textbook. The repository is useful for software engineers preparing for system design interviews or reviewing distributed systems fundamentals. Its main value is providing structured, accessible notes that make large architecture topics easier to revisit.