Although testbeds and experimental facilities are accepted as tools for research in the scope of distributed systems research, such as Future Internet Research, they lack sustainability; once established as a project, they must be maintained and renewed every few years. However, unfortunately, due to an absence of long-term funding for operating/maintenance and reinvestment, a lot of these are terminated just after the project is complete. In this paper, we describe a software-defined testbed on demand; this is based on the Topology Management Tool (ToMaTo), a software environment which was developed within the G-Lab project. ToMaTo, initially designed to run on the G-Lab infrastructure, is now independent of the underlying infrastructure and can be deployed on any Cloud infrastructure on demand. We describe here the deployment of ToMaTo to the CloudLab infrastructure offered by the NSF-funded CloudLab project. This approach offers a new method for sustainable testbeds where neither upfront investment nor the recurring and operating/maintenance costs for the infrastructure will burden the budgets of the projects.