Shopify's core Rails app had grown to 2.8 million lines of code and 500,000 commits, with hundreds of developers adding features simultaneously. Rather than migrate to microservices, they chose a harder path: make the monolith itself modular.
Required Knowledge
Monolith - a single application where all the code lives and runs together. Simple to start, harder to manage as it grows.
Microservices - splitting an application into many small, independent services that each handle one thing. More flexible at scale, but far more complex to operate.
Dependency - when one piece of code relies on another to work. Too many dependencies between parts of a system makes it hard to change anything without breaking something else.
Static analysis - examining code without running it. Tools can read your source files and flag problems - like a spell checker, but for code structure.
Component - a self-contained section of the codebase with a clear boundary and a defined owner. The goal of Shopify's effort was to carve their monolith into components.
My Key Takeaways
Keeping everything in one codebase is harder to organise, but avoids the enormous complexity of running dozens of separate services
Getting hundreds of engineers to change how they work is harder than any technical problem - you have to make the right way feel easy, not forced
If every part of your code depends on every other part, clean separation is impossible - untangling those connections matters as much as drawing good boundaries
Catching problems by scanning code before it runs is far more useful than discovering them later - faster feedback with less noise
Good structure at a large scale only works if the small-scale code is also well-organised - messy internals will always bleed through any boundary you draw