The Architecture Decision That Haunts Startups
Nothing has killed more promising SaaS products than premature microservices. A startup with 3 engineers, 50 customers, and $0 in profit should not be operating a distributed system of 12 services. And yet, thanks to tech blog hype, it keeps happening.
The Case for Starting with a Monolith
A monolith is a single deployable unit containing all your application logic. For most SaaS companies from $0 to $10M ARR, this is the right architecture. Why?
- Simpler debugging: One codebase, one set of logs, one deploy
- Faster iteration: No inter-service API contracts to maintain
- Lower infrastructure cost: One database, one server
- Easier for small teams: No need for DevOps expertise
The Modular Monolith: Best of Both Worlds
The modular monolith gives you clean separation of concerns without distributed system complexity. Organize your code into modules (billing, users, AI, notifications) with explicit interfaces between them. When you need to extract a module into a microservice, the boundaries are already defined.
src/
modules/
billing/ (Stripe logic, subscription management)
ai/ (LLM calls, prompt management)
auth/ (user management, permissions)
notifications/ (email, webhook delivery)When to Move to Microservices
Migrate individual components to separate services when: specific components have different scaling needs (AI inference needs GPU, your API doesn't), you need technology isolation (Python ML code separate from TypeScript API), team size grows beyond 20–30 engineers working on same codebase.
The Anti-Pattern: Premature Microservices
Signs you're over-engineering: you have more services than engineers, you spend more time on service communication than features, debugging requires reading logs across 5 systems, your CI/CD pipeline for a 2-line change takes 20 minutes. Start simple. Scale when the pain is real.