Module 17: Multi-Tenant SaaS Architecture

🚀 Problem Statement

An Enterprise Platform serves 50 organizations. Each organization requires data isolation, custom branding, different compliance requirements (some requiring data in the EU, others in the AU), and the ability to use their own cloud AI instances. Managing 50 separate deployments is operationally unsustainable.

🧠 The Engineering Story

The Villain: "The Deployment Factory." Assigning each customer their own Kubernetes namespace, database, and Redis instance results in managing dozens of parallel environments. A single security patch then requires dozens of deployments.

The Hero: "The Shared-Nothing Logical Isolation." One deployment, but with tenant-aware routing, row-level security in the database, and per-tenant configuration for LLM providers.

The Plot:

1. Tenant isolation models: siloed (separate DB per tenant) vs pooled (shared DB, row-level security) vs hybrid
2. Per-tenant configuration: LLM provider, model version, rate limits, feature flags
3. Data residency: route tenant data to region-specific storage
4. Noisy neighbor prevention: per-tenant resource quotas

The Twist (Failure): The Cross-Tenant Leak. A bug in the query filter causes one organization to see another's enterprise documents. In a pooled tenancy model used for cost savings, the blast radius of such a leak can be catastrophic, whereas in a siloed model, it would be physically impossible.

Interview Signal: Can articulate the security vs cost trade-offs of each tenancy model.