For many years Reactive systems were a niche solution that helped a handful of companies that had harder problems than everyone else to solve. For everyone else, Reactive was a solution looking for a problem. Well that problem has now arrived in the mainstream. Serverless platforms may well abstract away the responsibility of developers and administrators to run and maintain servers, but for a system to work in that environment, it has to be architected to handle that. It has to stay responsive when platform automation underneath it is scaling up, scaling down, rebalancing, applying updates, and failing as all systems fail. Serverless is the perfect problem that Reactive architectural patterns were designed to solve. In this talk we'll run through how Lightbend's new Reactive serverless offering, Kalix, makes building reactive systems on a serverless platform simple, by abstracting away state as a platform managed resource, and allowing developers to write Reactive systems that need only focus on the business logic of their application.