Architecting a Multi-Tenant SaaS Engine with Next.js & PostgreSQL

Designing a multi-tenant SaaS application requires balancing data security, operational costs, and query performance. Here is how we build horizontally scalable multi-tenant platforms. ### Tenant Isolation Strategies * **Database per Tenant:** Maximum security and simple backups, but costly and complex to migrate across hundreds of schemas. * **Schema per Tenant:** Good isolation, but database migrations become slow at scale. * **Shared Database, Row-Level Security (RLS):** Optimal scalability. Every table enforces a tenant identifier through PostgreSQL Row Level Security policies. --- ### Edge Tenant Routing in Next.js ```typescript // middleware.ts - Tenant Context Extraction import { NextResponse } from 'next/server'; import type { NextRequest } from 'next/server'; export function middleware(req: NextRequest) { const hostname = req.headers.get('host') || ''; const subdomain = hostname.split('.')[0]; const res = NextResponse.next(); res.headers.set('x-tenant-id', subdomain); return res; } ```