Microservices vs Monolith: What I Learned After Building Both

## The Architecture Decision That Matters Most I've built monolithic applications that scaled to millions of users. I've also built microservices architectures that were overkill for the team size. Here's what I learned. ### Start Monolith, Extract Later This is the advice most experienced engineers give, and it's correct. A well-structured monolith is easier to: - Develop (one codebase, one deployment) - Debug (one log stream, one database) - Test (integration tests are simpler) - Deploy (one artifact, one process) ### When to Consider Microservices **You need microservices when:** - Different parts of your app need different scaling - Teams are large enough to own separate services (5+ developers per service) - You need technology diversity (Python for ML, Node for APIs) - Parts of the system have very different deployment cycles **You DON'T need microservices when:** - Your team is small (< 10 developers) - The application is relatively simple - You're building an MVP - You don't have DevOps expertise ### The Hidden Costs of Microservices 1. **Network complexity** - services communicate over HTTP/gRPC 2. **Data consistency** - no more simple database joins 3. **Deployment complexity** - managing 15 deployments vs 1 4. **Debugging difficulty** - tracing requests across services 5. **Operational overhead** - monitoring, logging, alerting for each service ### The Pragmatic Approach: Modular Monolith Structure your monolith like it could become microservices: ``` src/ modules/ users/ controllers/ services/ models/ orders/ controllers/ services/ models/ payments/ controllers/ services/ models/ ``` Each module has clear boundaries. When (if) you need to extract a service, the code is already organized. **Architecture should serve your team, not the other way around.**