Low-Level Design for MAANG Interviews

A book-shaped table of contents for LLD interview prep: OOP fundamentals through SOLID, design principles, UML, design patterns, dependency management, reliability, concurrency, domain modeling, API design, testing, refactoring, classic interview problems, advanced architecture, and performance — cross-linking Object-Oriented Programming and Patterns instead of duplicating them.

1 — Hexagonal Architecture

Isolates core domain logic behind ports and adapters so infrastructure choices like databases or messaging can be swapped without touching business rules.

2 — Clean Architecture

Layers a system into entities, use cases, interface adapters, and frameworks so dependencies always point inward toward stable business rules.

4 — Event-Driven Design

Decouples components by having them communicate through published events rather than direct calls, trading immediate consistency for looser coupling.

5 — CQRS Basics

Splits read and write models into separate paths so each can be optimized and scaled independently instead of sharing one general-purpose model.