Notes on designing systems that survive real traffic: scaling strategies, databases under load, caching, communication patterns, and the trade-offs behind every architectural decision.
The notes here cover the foundations, database performance, caching at every level, scaling strategies, delegation, concurrency, and communication patterns, along with high-level design and relational databases. If you are starting from scratch, Learning Sources collects the free courses, books, engineering blogs, and papers worth working through, in the order I would work through them.