Maxime Vaillancourt shared the background and details of how Shopify reduced their storefront response times with a rewrite.

The Rails monolith still handles checkout, admin, and API traffic, but storefront traffic is handled by the new implementation.

Designing the new storefront implementation from the ground up allowed us to think about the guarantees we could provide: we took the opportunity of this evergreen project to set us up on strong primitives that can be extended in the future, which would have been much more difficult to retrofit in the legacy implementation. An example of these foundations is the decision to design the new implementation on top of an active-active replication setup. As a result, the new implementation always reads from dedicated read replicas, improving performance and reducing load on the primary writers.

Similarly, by rebuilding and extracting the storefront-related code in a dedicated application, we took the opportunity to think about building the best developer experience possible: great debugging tools, simple onboarding setup, welcoming documentation, and so on.