In this talk we'll consider a real case with Haskell in production. I'll tell you how we were migrating a big codebase from Ruby to Haskell, why Ruby stopped to satisfy our needs and how Haskell could help here. I'll describe a particular design decisions have been taken for the most of the day-to-day needs: REST service API, JSON serialization, subsystem interfaces, business logic and implementation separation etc., and what libraries have been used for this.