How I built multi-tenant Row Level Security with Aurora PostgreSQL for a B2B SaaS — H0 Hackathon

I'll be honest: I almost did multi-tenancy the wrong way. When I started building InspectIQ "a SaaS platform for Florida home inspectors" my first instinct was to add a tenant_id column to every table and filter it in the application layer. Every query would have a WHERE tenant_id = :current_tenant clause. Simple, familiar, done. Then I thought about what happens when you forget one. One missing WHERE clause. One endpoint that skips the filter. One inspector sees another inspector's client data. In a home inspection business, that's not just a bug — it's a HIPAA-adjacent nightmare and a trust-destroying moment with your first customer. So I did it properly from day one: Row Level Security at the database layer. What is Row Level Security? RLS is a PostgreSQL feature that lets you define policies directly on tables. When a user queries a table, the policy runs automatically, before your application code even sees the results. You can't forget to apply it. You can't bypass it with a careless JOIN. It's enforced at the lowest possible layer. For a multi-tenant SaaS, this is exactly what you want. How I implemented it Every table in InspectIQ has this pattern: ALTER TABLE inspections ENABLE ROW LEVEL SECURITY ; ALTER TABLE inspections FORCE ROW LEVEL SECURITY ; CREATE POLICY tenant_isolation ON inspections USING ( tenant_id = NULLIF ( current_setting ( 'app.current_tenant_id' , true ), '' ):: uuid ); The FORCE is important — it applies the policy even to the table owner. No superuser backdoor. The tenant context comes from the JWT. When an inspector logs in, their tenant_id is embedded as a custom Cognito claim. The FastAPI middleware extracts it and sets it at the start of every request: await session . execute ( text ( f " SET LOCAL app.current_tenant_id = ' { tenant_id } '" ) ) SET LOCAL scopes the setting to the current transaction. When the transaction ends, it's gone. No leakage between requests. Aurora PostgreSQL Serverless v2 I'm running this on Aurora PostgreSQ