A Virtual Machine Re-packing Approach to the Horizontal vs. Vertical Elasticity Trade-off for Cloud Autoscaling

An automated solution to horizontal vs. vertical elastic-ity problem is central to make cloud autoscalers truly au-tonomous. Today’s cloud autoscalers are typically varying the capacity allocated by increasing and decreasing the num-ber of virtual machines (VMs) of a predefined size (horizon-tal elasticity), not taking into account that as load varies it may be advantageous not only to vary the number but also the size of VMs (vertical elasticity). We analyze the price/performance effects achieved by different strategies for selecting VM-sizes for handling increasing load and we pro-pose a cost-benefit based approach to determine when to (partly) replace a current set of VMs with a different set. We evaluate our repacking approach in combination with different auto-scaling strategies. Our results show a range of 7 % up to 60 % cost saving in total resource utilization cost of our sample applications and workloads