Current inter-data-center connections are configured as static big fat pipes, which entails large bit rate over-provisioning and thus high operational costs for DC operators. On the other hand, network operators cannot share such connections between customers, because DC traffic varies greatly over time. Those connections are used to perform virtual machine migration and database synchronization among federated DCs, allowing elastic DC operations. To improve resource utilization and save costs, dynamic inter-DC connectivity is currently being targeted from a research point of view and in standardization form. In this article, we show that dynamic connectivity is not enough to guarantee elastic DC operations and might lead to poor performance provided that not enough overprovisioning of network resources is performed. To alleviate it to some extent, we propose using the flexgrid optical technology that enables finer spectrum granularity adaptation and the ability to dynamically increase and decrease the amount of optical resources assigned to connections. DCs can be interconnected through a flexgrid-based network controlled using a centralized software defined network, based on the architecture currently being proposed by the IETF; a cross-stratum orchestrator architecture coordinates DC and network elastically. Illustrative results show that dynamic elastic connectivity provides benefits by reducing the amount of overprovisioned network resources and facilitating elastic DC operations.

The research leading to these results has received funding from the European Community’s Seventh Framework Pro- gramme FP7/2007-2013 under grant agreement no. 317999 IDEALIST project. Moreover, it was supported by the Span- ish science ministry through the TEC2011-27310 ELASTIC project.