# What Multi-Tenancy Means — Multi-Tenant SaaS Architecture

Source: https://www.skillbyai.com/en/multi-tenant-saas/mt-what-is-multi-tenancy

> Define a tenant, explain how one running SaaS system serves many customer organisations, and name what tenants share and what they must never share.

## One system, many customers

A **tenant** is a customer organisation that uses your software as its own isolated space: a company, a school, a clinic. **Multi-tenancy** means a single deployed system serves many tenants at once, instead of installing a separate copy of the product for each customer. Tenants usually share the code, the servers and often the database, but each tenant must see only its own data, users and settings. That split is the whole game. Sharing is what makes SaaS cheap to run: one deployment to patch, one fleet to monitor, hardware used by many customers whose peaks rarely line up. Isolation is what makes it trustworthy: a bug or a heavy workload from one customer must not leak data to, or slow down, another. Every design decision in this course is a trade-off between how much you share and how strongly you isolate.

## The shared-but-isolated picture

Requests from many tenants arrive at one product. The platform identifies the tenant, then routes the work to that tenant's slice of shared or dedicated resources.

![Three connected stages: requests from many tenants, a shared application layer that identifies each tenant, and per-tenant isolated data.](assets/figures/multi-tenant-saas/section-1-map.svg) — Figure 1.1: tenant requests -> shared application (identify tenant) -> isolated tenant data

## A housing society

A multi-tenant SaaS is like a gated apartment society. Everyone shares the lift, the security gate, the water tank and the maintenance staff, so each flat pays far less than an independent bungalow would. But every flat has its own lock. The society works only if the shared parts are fair and no key ever opens a neighbour's door.

## Tenant is not a technical unit

Students often equate a tenant with a database or a server. A tenant is a *business* boundary: the customer who signs the contract and owns the data. How you map that tenant to databases, schemas or servers is a separate, changeable design choice that later sections cover.

**Quiz:** Which statement best describes multi-tenancy?

- [ ] Every customer gets a separately installed copy of the application
- [x] One deployed system serves many customer organisations while keeping their data and settings isolated
- [ ] Multiple users can log in to the same account with one password
- [ ] The application runs in several cloud regions at the same time

*Answer:* One deployed system serves many customer organisations while keeping their data and settings isolated. Multi-tenancy is about many customer organisations sharing one running system with logical isolation. Separate installs per customer is single-tenant hosting; multi-region is about availability, not tenancy.