Most SaaS applications start with a simple and familiar multi-tenant model: one shared backend one shared runtime one shared process tenant separation handled mostly by application code a tenant_id column or some equivalent logical boundary This model works well in many cases, especially at the beginning. It is simple. It is cheap. It is fast to build. It fits naturally into most web frameworks. But as a SaaS product grows, especially when it becomes white-label, extensible, or customer-specific, this approach can become fragile. A bug in one tenant can affect others. A bad customization can break the whole service. A plugin or custom app can access more than it should. A single shared process can increase the blast radius of failures. At some point, tenant isolation stops being only an application concern. It becomes an operational concern too. Logical multi-tenancy is not enough for every case Logical multi-tenancy usually means that the application is responsible for keeping tenants separated.…