The document discusses SoundCloud's transition from a monolithic Rails application to a microservices architecture. It describes how SoundCloud started on Rails which led to a monolith, challenges with large monolithic teams, and the steps taken to split into independent services including stabilizing the existing app, creating interface guidelines, minimizing overhead, and making deployments easy. The transition involved moving some services to other languages like Clojure, Scala and Ruby while reducing pull request times and moving to smaller independent teams.