Why Paying for Storage Beats Free Networking in Cloud Bursting

Hybrid cloud applications elastically burst to public clouds from an on-premise private cloud. In this setup only the public cloud directly charges applications for storing and processing data while the on-premise storage and network are already paid for and hence are considered free of charge. Consequently, application designers are naturally inclined to store and serve data remotely, while only paying for compute in the public cloud. In this work we claim, perhaps counter-intuitively, that it is often the case that hybrid cloud applications should pay for cloud storage that is co-located with the cloud computations as a mean to reduce overall costs. A co-located cloud storage can serve as a cache for frequently-accessed data and help minimize data transfers from the on-premise cloud over relatively slow inter-cloud networks. This practice can implicitly reduce the public cloud compute charges by reducing wait time of remote reads from the on-premise location, which more than compensates for the increase in cloud storage costs. We demonstrate the potential benefits of our proposed caching scheme for two elastic computing models, on-demand and serverless, and multiple cache policies that utilize a cloud-resident object storage service. Our evaluation, based on cloud object store traces, suggests that this method can achieve substantial cost reduction, at times reducing costs by up to 85%.