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Everyone talks about microservices when the system gets big.
Shopify went in a different direction, and there is a lot .NET developers can learn from that.

In this video, I break down how Shopify evolved its architecture into a modular monolith, why that decision made sense at their scale, and what lessons apply directly to building large systems in .NET.

We go beyond the usual monolith vs microservices debate and focus on the real architectural issues that matter: boundaries, coupling, cohesion, and how to keep a large codebase maintainable as teams and complexity grow.

What we cover:

- Why Shopify is such an interesting architecture case study
- The difference between a traditional monolith and a modular monolith
- Why internal boundaries matter more than most teams realize
- The problems caused by tight coupling in large systems
- How modularity improves maintainability and team autonomy
- The tradeoffs between modular monoliths and microservices
- What .NET developers can apply in their own applications
- Why scale does not automatically mean you need microservices

This is a practical breakdown for developers and architects who want to build systems that scale without creating unnecessary complexity.

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Chapters

We Are .NET

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.

Why Shopify Rejected Microservices (And What They Did Instead)