What is Multi-tenancy?
Multi-tenancy is the SaaS architecture pattern where one application serves multiple isolated customer accounts (tenants) from a shared codebase.
Definition
Multi-tenancy is the foundational architecture pattern of every B2B SaaS product. One application, one codebase, one deployment — serving N isolated customer accounts (tenants). The three sub-patterns: shared schema (one database, every row scoped by tenant_id — most common), schema-per-tenant (one database, one schema per tenant — better isolation), and database-per-tenant (full isolation — used for compliance-heavy verticals). Done right: row-level security by construction, audit logs scoped per tenant, no possibility of cross-tenant data leakage. Done wrong: a single SQL bug exposes one customer's data to another.
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