Multi-tenancy is the architectural pattern that lets a single application serve many customers from shared infrastructure. Done well, it lowers cost, simplifies operations, and accelerates onboarding.
Three Tenant Isolation Models
You can isolate tenants at the row level, the schema level, or the database level. Row level is cheapest but couples blast radius across tenants. Database per tenant gives the strongest isolation but raises operational complexity.
The Hidden Cost of Noisy Neighbors
Shared resources mean one tenant can starve another. Plan for per-tenant rate limits, query budgets, and capacity planning from day one.
Identity and Authorization
Every request must answer two questions: who is the user and which tenant are they acting on. Bake tenant context into your auth layer rather than scattering checks through your handlers.
Conclusion
Pick the lightest isolation model that meets your compliance and performance needs. You can always move heavier later, but you cannot retrofit security after a breach.