Multi-Tenant Architecture Patterns for B2B SaaS
A deep-dive into silo, pool, and hybrid tenancy models — and how RCWMAS chose its isolation strategy across six products.
Tenancy Models: A Framework
Every B2B SaaS application must make a fundamental architectural decision before writing the first line of data logic: how does the system isolate data and operations between its tenants?
The answer determines performance ceilings, cost floors, compliance posture, and the complexity of every data-related feature you will build for the lifetime of the product. Getting it wrong is expensive to reverse.
This whitepaper presents the three primary tenancy models, the conditions under which each is appropriate, and the hybrid approach that RCWMAS uses across its six-product portfolio.
The Silo Model
In a silo (or isolated) tenancy model, each tenant has a completely separate database — sometimes a separate application stack. Data isolation is absolute by construction.
When to use it:
Tradeoffs:
The Pool Model
In a pool (or shared) tenancy model, all tenants share a single database with a tenant_id column as the isolation boundary. Data isolation is enforced by application logic and query filters.
When to use it:
Risk:
WHERE tenant_id = ? clause is a data breach. This risk must be managed architecturally, not just through code review.The Hybrid Model
A hybrid model allocates tenants to tiers based on their characteristics. Small tenants share a pooled tier; large or regulated tenants are promoted to an isolated silo automatically or on-demand.
This is the model we use at RCWMAS. It allows us to serve the long tail of smaller customers cost-effectively while meeting enterprise and compliance requirements for larger customers without architectural compromise.
Row-Level Security as Architecture
For the pooled tier, PostgreSQL's Row-Level Security feature provides a strong architectural guarantee against cross-tenant data access — moving the tenancy enforcement from application code into the database layer.
CREATE POLICY tenant_isolation ON documents
USING (tenant_id = current_setting('app.current_tenant')::uuid);
This approach means a query that forgets the tenant filter fails silently rather than returning cross-tenant data — a significant improvement in the risk profile for pooled architectures.
Migration Considerations
Moving an existing product from pool to silo as a tenant grows is one of the most disruptive operations in B2B SaaS. Planning the data portability model from day one — even if you begin with pooled tenancy — dramatically reduces the cost of this transition later.
RCWMAS builds and operates multi-tenant platforms across legal, construction, and infrastructure verticals.