While an extensive set of research project deals with the saving power problem of electronic devices powered by electric battery, few have interest in large scale distributed systems permanently plugged in the wall socket. However, a rapid study shows that each computer, member of a distributed system platform, consume a substantial quantity of power especially when those resources are idle. Today, given the number of processing resources involved in large scale computing infrastructure, we are convinced that we can save a lot of electric power by applying what we called green policies. Those policies, introduced in this article, propose to alternatively switch On and Off computer nodes in a clever way.