Chatty Tenants and the Cloud Network Sharing Problem

The emerging ecosystem of cloud applications leads to significant inter-tenant communication across a datacenter’s internal network. This poses new challenges for cloud network sharing. Richer inter-tenant traffic patterns make it hard to offer minimum bandwidth guarantees to tenants. Further, for communication between economically distinct entities, it is not clear whose payment should dictate the network allocation. Motivated by this, we study how a cloud network that carries both intra- and inter-tenant traffic should be shared. We argue for network allocations to be dictated by the least-paying of communication partners. This, when combined with careful VM placement, achieves the complementary goals of providing tenants with minimum bandwidth guarantees while bounding their maximum network impact. Through a prototype deployment and large-scale simulations, we show that minimum bandwidth guarantees, apart from helping tenants achieve predictable performance, also improve overall datacenter throughput. Further, bounding a tenant’s maximum impact mitigates malicious behavior.Hadrian will not be the last word in fair bandwidth management for inter-tenant communication, of course. Many unresolved questions remain, such as whether there are other less-obvious incentive compatibility issues or vulnerabilities to abuse that the proposed scheme leaves un-addressed, such as other variants of Sybil attacks. The paper clearly suggests opportunities for future synergistic research in modeling and formally analyzing the robustness of this and similar schemes to arbitrary strategic behaviors by tenants. The paper also leaves some important practical questions to future work, such as how to manage fair allocation for services likely to be used by most or all tenants, such as central storage services offered by the cloud infrastructure provider. In general, even if not the last word, the NSDI PC felt that this paper represents a clear, principled, and compelling step forward toward a deeper understanding of fair communication resource allocation mechanisms to manage today's and tomorrow's tangled stacks of interdependent cloud-based services.