Debunking Real-Time Pricing in Cloud Computing

Elasticity of cloud computing eases the burden of capacity planning. Cloud computing users dynamically provision IT resources tracking their fluctuating demand, and only pay for their usage. Therefore, cloud computing essentially shifts the burden of capacity planning from user's side to provider's side. On the other hand, providers take this burden with the optimistic assumption that diverse workloads from various users will flatten the overall demand curve. However, this optimistic hypothesis has not been proved yet in the real world cases. In fact, counter evidences have been raised. December 2009, Amazon Web Services (AWS), a leading infrastructure cloud service provider, started to offer a real-time pricing for computing resources -- Amazon EC2 Spot Instances (SIs). Real-time pricing, in principle, encourages users to shift their flexible workloads from provider's peak hours to off-peak hours with monetary incentives. Interestingly, from our observation on AWS's one-year SI price history datasets, we conclude that the observed monetary incentive is not large enough to motivate users to shift their workloads. It is reasonable for users to choose SIs over on-demand instances because SIs are 52.3% cheaper on average. After that, shifting the workload to cheaper period provides only 3.7 % additional cost savings at best. Moreover, both average cost savings and price fluctuation have not been meaningfully changed over time.