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.