Multi-Tenant SaaS Architecture: Choices and Costs in Dublin

The verdict in three sentences

For a vendor growing from 5 to 80 customers, a shared database isolated by tenant ID remains the best balance of cost and simplicity, around EUR 0.80 to 1.50 per tenant per month. A schema per customer or a dedicated database is justified for enterprise accounts demanding contractual isolation, at EUR 3 to 6 per tenant. The architecture rebuild costs EUR 40,000 to 100,000 excluding VAT over 3 to 5 months, and a hybrid model is often the most profitable answer.

The context: a Dublin vendor changing scale

Thomas, CTO of a Dublin-based vendor of management software for shipping and port logistics companies, started with 5 customers, each on a hand-copied instance. With 80 customers signed or in the pipeline, including two port groups imposing a security annex, the model is unsustainable: 80 deployments, 80 database migrations, diverging versions.

The three multi-tenant models compared

With PostgreSQL, Row Level Security makes a shared database far more robust than an application filter alone: even a badly written query cannot read another customer's data. It is the recommended foundation for most tenants.

The hybrid model, a pragmatic answer

Most B2B vendors serving both SMEs and enterprises adopt a hybrid model: shared database for 90 to 95% of customers, a dedicated database sold as an "Enterprise" option to accounts that require it. The application resolves the database connection from the tenant, so a customer can move between models without a rewrite.

The work is done customer by customer, with progressive cutover and rollback available. No outage beyond an overnight maintenance window should be accepted.

What enterprise accounts really ask for

Security questionnaires from port and industrial groups always return to the same points: data residency in the EU, encryption at rest, isolation, reversibility, access logging. A dedicated database in an EU region ticks the isolation box without debate. It is usually billed at EUR 300 to 800 a month on top of the subscription, which easily covers its real cost of EUR 3 to 6 in infrastructure plus operating time.

Mini case study

Thomas chooses the hybrid model: 76 customers on the shared database at EUR 1.20 a month, 4 enterprise accounts on dedicated databases at EUR 5 a month. Infrastructure: 76 × 1.20 + 4 × 5 = EUR 111.20 a month, versus about EUR 480 for 80 separate instances. The rebuild costs EUR 68,000 over 4 months. The 4 enterprise accounts each pay a EUR 500 monthly Enterprise option, EUR 24,000 a year. Added to infrastructure savings (about EUR 4,400 a year) and the 2 days a month of manual deployments eliminated (about EUR 14,400 a year at EUR 600 a day), the rebuild pays back in just under 20 months.

FAQ

Which multi-tenant model for a B2B SaaS?

A shared database with Row Level Security fits most cases, at EUR 0.80 to 1.50 per tenant per month. Add dedicated databases only for customers who require them contractually.

How much does a multi-tenant rebuild cost?

Allow EUR 40,000 to 100,000 excluding VAT and 3 to 5 months for a vendor with 50 to 100 customers. Migrating existing data is the most variable item.

Is a shared database secure enough for enterprises?

With RLS, encryption and audits, technically yes. But 30 to 50% of enterprise accounts require physical isolation in their annexes, hence the dedicated database option.

Can we migrate without downtime?

Yes, by moving customers one at a time with temporary dual writes or a 1 to 2 hour overnight window. A per-tenant rollback plan is essential.

Should the dedicated database be billed?

Yes, an option at EUR 300 to 800 a month is common. It covers infrastructure, monitoring and individual backups.

Let's scope your project. We audit your current architecture and price the multi-tenant rebuild at EUR 40,000 to 100,000, with progressive cutover over 3 to 5 months. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.