Discuss Microservices vs. Monolith Architecture

A monolithic architecture bundles all application logic into a single codebase and deployment unit, making it ideal for startups due to its simplicity in testing and debugging. In contrast, microservices decompose the system into loosely coupled, independently deployable services that communicate via APIs. The primary advantage of microservices is scalability; you can scale specific high-load components without replicating the entire app, and teams can work autonomously. However, this introduces significant complexity in distributed tracing, data consistency, and network latency. Monoliths suffer from the opposite: they are hard to scale horizontally and prone to cascading failures, but they offer rapid iteration speeds initially. A monolith should be broken down when the organization outgrows the 'two-pizza team' rule, typically around 10-15 developers per service area, or when different modules require vastly different scaling characteristics, such as a video processing engine needing GPU resources while the user profile service does not. At Meta, we often start monolithic to validate an idea quickly, then incrementally extract services only when the cost of coordination exceeds the benefits of modularity.