Cloud Computing promises to completely revolutionize the capacity management of resources. The elasticity and the economy of scale are the intrinsic elements that differentiate it from traditional computing paradigm. A good capacity planning method is a necessary factor but not sufficient to fully exploit Cloud elasticity. This paper proposes innovative policies for resource management to achieve the optimal balance between capacity and quality of Cloud services while supporting Cloud technical and conceptual limitations. The main idea is to control finely the scalability and the termination of virtual machines in regards of several criteria such as the lifecycle of the instances (e.g. initialization time) or their cost. The approach was evaluated with a real infrastructure (Amazon EC2) and an application testbed. Experimental results illustrate the soundness of the proposed approach and the impact of scalability/termination resource policies. Using DeltaScaling, the cost saving of as much as 30% can be achieved while causing the minimum number of violations, as small as 1%.