: This paper explains how we have designed a service-oriented architecture by combining and extending several open source environments. We show how the IT architecture of the National Family Benefits Fund in Luxembourg got systematically modernized by solving issues related to Enterprise Application Integration, before introducing concepts like Enterprise Service Bus which was extended to offer service orchestration and business workflow support. By taking advantage of Model Driven Software Design and by introducing a framework for adding new components to the service bus, technical burdens to get used to the new IT environment got minimized. The cost saving due to the open source subsystems and the ease of use make the proposed architecture particularly interesting for small and medium organizations.