Tenant Isolation

Tenant isolation is the set of controls that keep one customer's data, compute, and configuration from ever leaking into another's inside a multi-tenant SaaS app. Because you serve many organizations from shared infrastructure, a single missing WHERE clause, a mis-scoped cache key, or a leaky background job can expose one tenant's records to another — one of the most damaging bugs a SaaS can ship. Isolation runs on a spectrum: logical isolation (a shared database with a tenant_id column enforced by row-level security), schema-per-tenant, or full physical isolation (separate databases or clusters per customer). Stronger isolation costs more to run but is easier to prove to security reviewers. Practical note: enforce the tenant boundary in one place — middleware or a query scope — rather than trusting every developer to remember it, add automated tests that assert cross-tenant reads fail, and treat any cross-tenant leak as a Sev-1 incident.