On the impact of indirect WAN routing on geo-replicated storage

Micro-clouds infrastructures allow supporting applications on local and energy-efficient resources. Communication between micro-clouds takes place on shared and non-dedicated Internet links. Network control and optimization can only happen at the edge. For availability and persistence, the storage of application data must be geo-replicated. Maintaining strong data consistency under concurrent accesses requires delay-sensitive coherence protocols, linking the performance of the storage to that of the network between micro-clouds. We evaluate if the use of network control at the edge of a European-wide multi-site testbed, together with appropriate network monitoring, can allow improving the performance of ZooKeeper, a strongly-consistent replicated store. Our approach leverages the indirect routing of coherence protocol traffic in the presence of network triangle equality violations. We analyze the impact on storage of variations in WAN performance, and show how the use of traffic redirection can help reducing it.