Design and Implementation of a Consistent Data Store for a Distributed SDN Control Plane

Scalable and fault-tolerant distributed Software-Defined Networking (SDN) controllers usually give up strong consistency for the network state, adopting instead the more efficient eventually consistent storage model. This decision is mostly due to the performance overhead of the strongly consistent replication protocols (e.g., Paxos, RAFT), which limits the responsiveness and scalability of network applications. Unfortunately, this lack of consistency leads to a complex programming model for network applications and can lead to network anomalies. In this paper we show how the lack of control plane consistency can lead to network problems and propose a distributed SDN control plane architecture to address this issue. Our modular architecture is supported by a fault-tolerant data store that provides the strong consistency properties necessary for transparent distribution of the control plane. In order to deal with the fundamental concern of such design, we apply a number of techniques tailored to SDN for optimizing the data store performance. To evaluate the impact of these techniques we analyze the workloads generated by three real SDN applications as they interact with the data store. Our results show a two-to four-fold improvement in latency and throughput, respectively, when compared with a non-optimized design.