Every SaaS company eventually meets the tenancy decision they deferred. Schema-per-tenant looked elegant at 50 customers and became a migration nightmare at 5,000. Row-level isolation seemed simple until the first enterprise customer demanded their own database.
Three models, picked deliberately
Row-level isolation with PostgreSQL RLS for the long tail. Schema-per-tenant for mid-market with compliance needs. Cluster-per-tenant for the strategic enterprise accounts. Most mature SaaS platforms run all three, and the architecture is built to move customers between them without downtime.
The boring decisions matter more
Billing, entitlements, SSO, audit logs, data export. Get these right early and they compound into trust. Get them wrong and they become rewrites at the worst possible moment.
Building with Unisam
As a senior custom software development services partner, we have shipped multi-tenant SaaS into healthcare, fintech and developer-tools verticals. The first slice ships in 90 days. The architecture survives Year 5.