Load migration in distributed softwarized network controllers

Distributed control solutions were introduced to address controller reliability and scalability issues in software-defined networking (SDN). The dynamic nature of network traffic can lead to load imbalance among controller instances. A highly loaded controller instance can be slow in responding to datapath queries and can slow down the entire control platform, as state synchronization and consensus among controller instances are performed in a cooperative manner. In this paper, we present Efficient, Resilient, Consistent (ERC), a novel protocol for migrating the load of a given switch from a controller instance to a different instance. Our protocol has three distinguishing properties compared with prior works in this area: (1) It is resilient to failures during migration, (2) it maintains consistency among all controller instances, and nevertheless, (3) it is more efficient than existing load migration protocols. Compared with state-of-the-art, ERC reduces the migration time by 23–50% depending on network load. The implicit assumed use case in the design of previous load migration algorithms (including ERC) has been the load balancing scenario. However, as this is not the only possible case, by maintaining the desirable properties of ERC, we introduce four variants of our protocol that can add to the versatility of the load migration handling. This is achieved by considering variations of role exchange between controller instances, which gives us an advantage over the fixed master–slave exchange that vanilla ERC or previous work support. We perform an extensive set of experiments to examine the impact of variable network parameters on the performance metrics of interest and to show the effectiveness of the ERC family of protocols in load migration.