The Complete SaaS Cookbook, Part 1: Architecture & Tech Stack

Why Most SaaS Architectures Fail

We've built and rescued enough SaaS products to know that architectural decisions made in the first two weeks determine 80% of the product's long-term velocity. Most founders get this wrong — not because they choose bad technology, but because they choose technology for the wrong reasons.

This 5-part series is the playbook we wish existed when we started building SaaS products. No theory — just the decisions, trade-offs, and patterns that actually work in production.

The Stack Decision Framework

Before choosing any technology, answer these three questions:

• What's your team's strongest language? A team that's excellent in Python will ship faster with Django than with a "theoretically superior" Go backend they're learning on the job
• What's your scaling timeline? If you need to support 100 users in 6 months, your architecture looks very different from supporting 100,000 users
• What's your hiring market? Choosing Elixir might be technically elegant, but hiring Elixir developers in Ho Chi Minh City is significantly harder than hiring TypeScript developers

Our Recommended Stack (2026)

For most B2B SaaS products, this is what we deploy:

Frontend: Next.js with TypeScript. Server components for SEO-critical pages, client components for interactive dashboards. Tailwind CSS for styling — it's not glamorous, but the velocity gains from utility-first CSS are undeniable at startup speed.

Backend: Next.js API routes for simple CRUD, separate NestJS or Hono service for complex business logic. TypeScript everywhere — the type safety across frontend and backend pays for itself within the first month.

Database: PostgreSQL. Full stop. It handles relational data, JSON documents, full-text search, and row-level security for multi-tenancy. You won't outgrow it until you're processing millions of transactions per day.

Infrastructure: Vercel for the frontend, Railway or Render for backend services, managed PostgreSQL (Supabase or Neon). Move to AWS/GCP only when you have a dedicated DevOps person.

Monolith First, Always

Start with a modular monolith. Not microservices. Not even a separate backend — unless your business logic genuinely can't fit in Next.js API routes.

The modular monolith approach means organizing your code into clear domain modules (users, billing, projects, notifications) with explicit boundaries between them, but deploying as a single application. When a module needs to become a service, the extraction is straightforward because the boundaries already exist.

"We've never seen a startup fail because they started with a monolith. We've seen many fail because they started with microservices before they understood their domain."

Project Structure That Scales

Here's the directory structure we use for every new SaaS project:

src/
  app/           # Next.js App Router pages
  modules/       # Domain modules
    auth/        # Authentication & authorization
    billing/     # Subscriptions & payments
    tenants/     # Multi-tenancy logic
    [feature]/   # Feature-specific modules
  lib/           # Shared utilities
  components/    # Shared UI components

Each module contains its own routes, services, types, and tests. Modules communicate through well-defined interfaces, never by importing each other's internals.

Critical Early Decisions

Three decisions you must make before writing any feature code:

• Multi-tenancy strategy: Shared database with tenant_id column (covered in Part 2) is the right choice for 95% of SaaS products
• Authentication approach: Use an auth library (Better Auth, NextAuth) or a managed service (Clerk, Auth0) — never roll your own
• Billing integration: Choose your payment provider (Stripe, Paddle, LemonSqueezy) early because it influences your data model (covered in Part 3)

In Part 2, we'll dive deep into authentication, authorization, and multi-tenancy — the trinity that makes or breaks every SaaS product.