Saru, a multi-tenant SaaS platform, uses PostgreSQL's Row-Level Security (RLS) to ensure data isolation across its 4-tier account structure. This approach, detailed in the latest article on the Saru Blog, addresses the challenge of maintaining data privacy in a complex hierarchy without relying solely on application logic. By implementing RLS, Saru can automatically filter data access, preventing forgotten WHERE clauses and missing permission checks that are common in solo development projects.

The article compares three data isolation patterns: database per tenant, schema per tenant, and shared schema with RLS. Saru opted for the shared schema approach, which offers low implementation and operational costs while providing high scalability. This method allows for simple operations and easy tenant management, though it requires careful RLS policy design and testing.

Saru's implementation includes setting RLS context using SET LOCAL in Go with pgx, creating policies for each tier, and verifying data visibility through integration tests. The author emphasizes the reassurance of having RLS as a 'last line of defense,' ensuring that even application bugs do not lead to data leaks. This article is part of a series that explores various aspects of Saru's architecture and development process.

For developers working on multi-tenant systems, this article offers practical insights into leveraging PostgreSQL RLS for data security and isolation. It underscores the importance of thorough testing and policy design in maintaining data integrity across complex tenant structures.