Why Shopify Rejected Microservices (And What They Did Instead)

Shopify runs its core platform as a modular monolith rather than microservices, handling 500M requests/minute at peak. Starting as a Rails MVC monolith with tightly coupled domains (billing, shipping, checkout, orders), they faced fragile code, slow tests, and high onboarding friction. Instead of migrating to microservices — which would add network overhead, multiple deployment pipelines, and cross-service data complexity — they reorganized ~6,000 classes into domain-based component folders, then enforced boundaries by exposing a public API per module and keeping implementations internal. Database-level separation via dedicated schemas per module further strengthens boundaries. The key insight is that modularity (high cohesion, controlled coupling) can be achieved in a single deployment unit, and the .NET ecosystem supports this pattern well using C# projects, internal access modifiers, and interfaces.