Horizontally scaling the Rails backend of Shop app with Vitess (2024)

We experienced hockey stick growth after we launched the Shop app. We were glued to our dashboards and saw millions of users onboard onto the app. This was gratifying, but we were becoming more nervous as our backend was pushed closer to its limit.We wrote the backend in Ruby on Rails, and used a MySQL database (Shopify managed system called KateSQL). The first order of business was to identify the bottlenecks. We iterated, horizontally scaling our background job system, caching system, and used a horizontally scaled Message bus where appropriate. We then invested into detecting the usual suspects: slow queries, limited connections etc. We also dropped the “The” from “The Shop app” because it was cleaner.