Why Modular SaaS Architecture Matters (And How to Build It)
Building a monolithic SaaS is fast at first, but painful at scale. Here's how modular architecture with feature flags and plugin systems keeps you agile.
Nova Team··5 min read
Every SaaS starts simple. Then it grows. Then it becomes impossible to change anything without breaking something else. The solution isn't microservices — it's modular monolith architecture with clean boundaries.
The monolith problem (and why microservices aren't the answer)
Most SaaS products start as monoliths. That's fine — monoliths are fast to build and easy to reason about at small scale.
The problem comes when:
Teams can't deploy independently
A billing bug breaks the AI feature
Disabling analytics for compliance reasons requires a code change + deploy
Enterprise customers need features others don't
The naive solution is microservices. But microservices add enormous operational overhead — distributed tracing, network latency, service discovery, versioned APIs between services. Most SaaS products shouldn't be microservices until they have 50+ engineers.
The better solution: modular monolith with feature isolation.
What modularity actually means
A modular SaaS is one where:
Features are isolated — code for billing doesn't depend on AI code
Features can be toggled — you can enable/disable a module at runtime
Modules are loaded on demand — unused features don't affect performance
Routes are conditional — disabled modules don't appear in navigation or URLs
You get the operational simplicity of a monolith with the flexibility of modules.
The plugin pattern
The most practical way to implement modularity is the plugin/module pattern:
When webhooks are disabled, the Webhooks nav item doesn't render. When AI is disabled, the AI Assistant link is gone. The user never encounters a dead end.
Route protection for disabled modules
Each module's routes should guard themselves:
// apps/web/src/app/dashboard/webhooks/page.tsx
export default async function WebhooksPage() {
const isEnabled = await getFeatureFlag('webhooks')
if (!isEnabled) redirect('/dashboard')
// ...rest of page
}
This makes the system self-consistent: whether you arrive via direct URL, link, or API — disabled modules are inaccessible.
Lazy loading for performance
Modules that contain heavy dependencies (AI SDKs, chart libraries) should be lazy-loaded:
Each module is a self-contained slice of the stack. Deleting a module folder and its route registration removes it entirely.
When to use this pattern
✅ Multi-tier SaaS (different plans get different features)
✅ B2B with enterprise customization requirements
✅ Products that will evolve significantly over time
✅ Teams > 3 engineers (avoid stepping on each other)
❌ Simple CRUD app with no tiers
❌ Internal tool with single user
❌ Prototype that needs to ship today (but build it in from the start)
The key insight
Modularity isn't about technology — it's about respecting product boundaries in your code. When billing code doesn't know about AI code, and AI code doesn't know about analytics code, you can change each one independently.
The SaaS Starter plugin system implements all of this out of the box. You can disable modules from the settings page and they disappear entirely — from the nav, from routes, from the bundle.
