Multi-Tenant SaaS Platform

Multi-Tenant SaaS Platform

Multi-tenancy lets one application instance serve many customers (tenants) while keeping their data and configuration isolated. It is the default model for business software-as-a-service because it pools infrastructure cost across tenants and lets you ship one codebase to all. Choose it for subscription B2B products. The central challenge is isolation: data, performance, and security boundaries between tenants must hold under all conditions. This design runs on Google Cloud.

Components

• Cloud Run: stateless application containers that autoscale per request.
• API Gateway: authenticates requests, enforces per-tenant rate limits, and routes traffic.
• Cloud SQL: relational storage using a tenant-discriminator column or a schema-per-tenant model.
• Identity Platform: federated sign-in, per-tenant identity providers, and token issuance.
• Pub/Sub: asynchronous events for provisioning, billing, and notifications.
• Redis (Memorystore): caches tenant config and hot data.
• Secret Manager: stores per-tenant keys and integration credentials.

Data Flow

A request arrives with a tenant identifier in its JWT. The gateway validates the token and attaches tenant context. Cloud Run resolves tenant configuration from cache, then queries Cloud SQL with the tenant filter applied at the data-access layer. Usage events publish to Pub/Sub, feeding metering and billing. Provisioning a new tenant runs an event-driven workflow that creates the tenant record, default config, and isolation boundary.

Scaling and Resilience

Cloud Run scales to zero and out under load. For very large or noisy tenants, a cell-based model places groups of tenants in separate stacks to contain blast radius and the noisy-neighbor effect. Enforce per-tenant quotas and rate limits so one tenant cannot starve others. Use read replicas for reporting. Stagger background jobs per tenant to smooth load.

Security

Isolation is the security property that matters most. Apply the tenant filter in a single, audited data-access layer — never rely on application code to remember it. Scope every token to one tenant and enforce least privilege on service accounts. Encrypt data at rest and in transit. Maintain an audit log per tenant for compliance frameworks such as SOC 2. Test cross-tenant access attempts continuously.

Trade-offs and Alternatives

Shared databases are cost-efficient but raise the stakes on isolation bugs; schema- or database-per-tenant strengthens isolation at higher cost and operational complexity. A cell-based hybrid balances the two. Single-tenant deployments suit a few high-compliance customers but lose the economics of pooling. Match the isolation model to your customers' risk profile and your cost targets.