"A complex system that works is invariably found to have evolved from a simple system that worked." (John Gall) - The evolvability of a software system is in many cases its most important architectural quality attribute. And an essential tactic to achieve this attribute is the localization of change by reusing domain boundaries as system and team boundaries. This talk discusses the application of this principle to big data systems and describes mobile.de's journey from a monolithic data architecture to a domain-driven data platform.