Abstract-One of the key promises of Cloud Computing is elasticity -applications have at their disposal a very large pool of resources from which they can allocate whatever they need. For any fair-size application the amount of resources is significant and both overprovisioning and under provisioning have a negative impact on the customer. In the first case it leads to over costs and in the second case to poor application performance with negative business repercussions as well. It is then an important problem to provision resources appropriately.In addition, it is well known that application workloads exhibit high variability over short time periods. This creates the necessity of having autonomic mechanisms that make resource management decisions in real time and optimizing both cost and performance. To address these problems we present and autonomic auto-scaling controller that based on the stream of measurements from the system maintains the optimal number of resources and responds efficiently to workload variations, without incurring in over costs for high churn of resources or short duration peaks in the workload.To evaluate the performance of our system we conducted extensive evaluations based on traces of real applications deployed in the cloud. Our results show significant improvements over existing techniques.