Building Production-Ready Multi-Tenant SaaS in Rust with Actix-web

I've been building SmartFarmAI, an AI-powered poultry farm management platform, and one of the hardest architectural decisions I had to make early on was: how do I safely isolate data between farms? When a farmer in Lagos logs in and checks their egg production numbers, they should never under any circumstance see data from a 60,000-bird enterprise operation in Tanzania. One bug, one missed WHERE clause, and you're leaking customer data. In agriculture, that's not just a privacy issue it's a business-ending trust violation. This article walks through exactly how I solved this using Rust, Actix-web, and PostgreSQL Row-Level Security (RLS) the patterns, the gotchas I hit in production, and the code that keeps it all safe. If you're building any kind of multi-tenant SaaS in Rust, this should save you weeks of trial and error. The pattern in a nutshell: Actix middleware extracts the tenant from each request, starts a DB transaction, calls SET LOCAL app.current_tenant_id, and lets Postgres