Public sector organizations around the world are embracing open source technologies to increase transparency, reduce vendor lock-in, and modernize service delivery. In this session, I present the Dutch government's approach to building sovereign, secure, and cloud-native infrastructure using open source. Drawing on our experience designing multi-tenant platforms across government data centers, I explore patterns, governance models, and lessons learned that are applicable to regulated environments globally. Also highlighted will be how our alignment with European digital sovereignty and open standards policies enables long-term resilience and innovation.