Public sector is a large consumer for software. In countries such as Finland, many of the systems are made to order by consultancy companies that participate in public tenders. These tenders initiated by the state, cities, and other public sector organizations. Furthermore, as public sector tasks are often decomposed to various actors, each and every one of them makes their purchase based on their own needs. In this paper, we argue that to maintain software sustainability in this context, there is a need for three key elements. Firstly, there is a need for an enterprise architecture where independent services from various vendors are can be easily deployed and integrated. Secondly, these services are build in a such manner that they can interact via well-defined APIs, but need no direct access to other services. Finally, techniques that support systematic, rapid development and deployment are needed.