What is the difference between a monolithic and microservices architecture?

Monolithic architecture: all application components (UI, business logic, data access) are in a single codebase, compiled and deployed together as one unit. Pros: simple development and debugging (single codebase), easy local development, simple deployment (one artifact), no network latency between components, simpler transactions (ACID). Cons: as it grows — hard to understand and modify, long build/deploy times, must deploy the whole app for a small change, one bug can crash everything, can't scale individual components (must scale the whole app), technology lock-in. Microservices architecture: application split into small, independent services each with its own codebase, data store, and deployment pipeline. Pros: independent deployment and scaling, technology flexibility per service, fault isolation (one service crash doesn't crash others), smaller codebases easier to understand, team autonomy. Cons: distributed system complexity, network latency between services, distributed transactions (no easy ACID), service discovery, operational overhead (many services to monitor), testing complexity. Migration path: start with a monolith (simpler, faster iteration early on); identify natural boundaries (domain-driven design); extract services as specific components need independent scaling, different technologies, or independent deployment. Strangler fig pattern: gradually migrate monolith to microservices by building the new service alongside the old, routing traffic incrementally.