What is Multi-Tenancy?

Multi-tenancy is an architecture where the same application code, and often the same infrastructure, serves multiple customers. Each customer is treated as a tenant; users, settings, data, plan limits, and billing rules must remain inside that tenant boundary.

The model is common in SaaS products because the team operates one product line instead of deploying a separate copy for every customer. Shared infrastructure, however, makes data isolation, authorization, and performance controls central design concerns.

Architecture Models

Shared database with tenant column: The lowest-cost model. Every row carries a tenant identifier, so query and permission checks must be strict.
Separate schema: Each tenant has its own schema on the same database server. Isolation improves, but operations become more complex.
Separate database: Useful for large customers or regulated workloads. It gives stronger isolation at higher cost and maintenance effort.

At the application level, tenant context may come from a domain name, session, JWT claim, or account selection. Every query, file access, background job, and analytics event needs to preserve that context.

Business Use

Multi-tenancy supports subscription plans, customer-specific feature flags, usage limits, and centralized updates. A new release can be deployed once while all customers benefit from the same product codebase.

The main risk is tenant data leakage. Tests should cover tenant isolation, admin panels must enforce permission boundaries, reports need safe filtering, and heavy tenants should not slow down others. Quotas, queues, and per-tenant monitoring help keep shared systems predictable.