Glossary

Multi-Tenancy

One software application serving many distinct customer organisations from shared infrastructure with isolated data.

Definition

Multi-tenancy is the architectural pattern where one running instance of an application serves multiple customer organisations (tenants), with each tenant's data and configuration isolated from the others. There are three common isolation models: row-level (a tenant_id column on shared tables), schema-per-tenant (separate database schemas per tenant), and database-per-tenant (a dedicated database per tenant). The choice has cascading effects on security posture, ops cost, performance isolation and migration complexity.

Why it matters

The isolation model is the most important architectural decision in early SaaS — it shapes the auth layer, the data layer, the billing layer, the admin tooling and the migration story. Reversing it later is expensive.

See also

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