Putting It All Together: A Reference Architecture for a GDPR-Compliant SaaS App

Enterprise buyers and public-sector organizations now routinely require SaaS products to keep data inside European borders. You can build a fast, secure, multi-tenant application hosted entirely on European providers like OVHcloud, Scaleway, and Hetzner. Open source components replace the proprietary US services that usually make up these stacks. The result costs less than an equivalent build on a major cloud provider while keeping all customer data resident and auditable.

Match Database Tenancy to Your Customer Requirements

How you separate tenant data shapes your database schema, billing logic, and security risks. A shared database with a tenant identifier on every row is cheap to run. It also puts the burden of isolation entirely on your application code, where one missing database filter leaks another customer’s data.

A schema-per-tenant model in PostgreSQL provides cleaner separation. It allows you to back up or migrate individual tenants, though connection overhead increases once you pass a few hundred schemas. A database-per-tenant approach isolates data completely for regulated customers, but operational load grows with every new account.

A hybrid approach fits most growing SaaS applications. You use pooled schemas for smaller accounts and dedicated databases for enterprise tenants paying for full isolation. Managed PostgreSQL on Scaleway or OVHcloud handles both patterns.

Run Compute Across Managed Clusters and Bare Metal

Containers running on Kubernetes work well for an application that needs to scale horizontally. Scaleway and OVHcloud both offer managed Kubernetes control planes with autoscaling node pools. They bill in euros, keep the control plane in an EU region, and use standard APIs to keep your configuration files portable.

For a smaller footprint without Kubernetes, Hetzner’s dedicated and cloud servers provide raw compute at low prices. You can run lighter alternatives like Nomad or Docker Compose behind a load balancer, taking on more operational work in exchange for cost savings.

A practical middle path uses managed Kubernetes on Scaleway for the stateless application tier. You then use Hetzner instances for heavy background workers where cost per core outweighs the need for orchestration.

Store Files and Deliver Content Locally

Store user uploads, generated reports, and static assets in object storage instead of local server disks. Scaleway Object Storage and OVHcloud Object Storage both use the standard S3 API, allowing your existing tools and software libraries to work without modification. You point your application to a European endpoint to ensure data stays in your selected region.

Both providers offer content delivery networks with European points of presence. If you need broader edge coverage, bunny.net operates a global CDN as a European company with strict data-handling terms. This keeps the entire delivery path under EU jurisdiction.

Replace Proprietary Services With Open Source Alternatives

Many teams stall when building on European infrastructure because they habitually reach for familiar proprietary services. Open source alternatives fill these gaps easily. OpenSearch or Meilisearch replaces hosted search platforms and runs directly on your servers. Redis and RabbitMQ handle caching and queues, and Scaleway offers both as managed services. European senders like Scaleway Transactional Email or Mailjet deliver transactional messages without passing customer contact data through US networks.

Authentication requires careful planning. Keycloak is an open source identity server that handles OAuth2, OpenID Connect, SAML, and multi-tenant accounts. Hosting it yourself keeps every user record and login event on European infrastructure. This satisfies the strict audit trails regulators expect.

For observability, use Prometheus for metrics, Grafana for dashboards, and Loki for logs. You can self-host these or run them as managed services on Scaleway. They provide deep visibility while keeping system telemetry inside your secure boundary.

Build Compliance Directly Into the Architecture

Keeping data resident is simple once you select European providers. Handling individual privacy rights and data lifecycles requires more effort. The right to erasure requires you to delete a user’s data on request. This includes removing data from backups within a defined window, as well as from search indexes and analytics stores. Treat deletion as a core feature that reaches into every data store.

Data portability requires exporting user records in a machine-readable format. An isolated tenancy model makes this export straightforward. If you use shared tables, you must write precise queries to extract one subject’s data without exposing another’s.

You must also log why you hold each piece of data and for how long. Keycloak’s event logs paired with an audit table in PostgreSQL create a precise record of data access. Scheduled jobs should enforce retention policies by deleting expired data automatically.

Legal agreements are also cleaner with European providers. OVHcloud, Scaleway, and Hetzner operate from EU-based legal entities and publish data processing addenda under EU law. This avoids the legal friction of using US-owned providers, even when those providers operate European data centers.

Assemble a Cost-Effective Sovereign Stack

In practice, this architecture routes incoming traffic through a European CDN to a load balancer in front of managed Kubernetes on Scaleway. The stateless application tier runs in containers. These containers connect to managed PostgreSQL, using pooled schemas for standard accounts and dedicated databases for enterprise customers.

Redis handles sessions and caching. RabbitMQ routes background jobs to worker nodes running on Hetzner. Object storage holds user files accessed through the S3 API, while Keycloak manages identity across all tenants. Prometheus, Grafana, and Loki monitor the entire system.

Every byte of customer data and every log entry remains on infrastructure governed entirely by European law. Monthly costs typically fall below equivalent setups on major cloud providers. Hetzner and Scaleway price their compute and bandwidth aggressively, making this architecture financially efficient. You gain full data sovereignty without sacrificing system performance or inflating your infrastructure budget.