Designing a multi-tenant system is one of the most critical architectural decisions for a SaaS startup. Get it right, and you scale with low marginal costs. Get it wrong, and you face data leaks and performance bottlenecks.
1. Database Isolation Strategies
There are three main ways to isolate tenant data:
- Database-per-tenant: High isolation, high cost.
- Schema-per-tenant: Balanced approach, but migration management can be tricky.
- Shared database, shared schema: Low cost, but requires rigorous row-level security (RLS) to prevent data leaks.
2. Row-Level Security in Action
With modern databases like PostgreSQL, you can enforce Row-Level Security directly at the database engine level. This ensures that even if a developer forgets to filter by tenant_id in their application query, the database will refuse to return other tenants' data.
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