A Simulated Annealing-based Efficient Failover Mechanism for Hierarchical SDN Controllers

The multi-controller architecture is a must to improve scalability and reliability of software defined networks (SDNs). A hierarchical multi-controller architecture allows a global controller to handle rare events, such as routing events from local controllers. A failover mechanism, which includes failure detection and recovery, is necessary for the multi-controller architecture in case of a controller failure. Existing controller failure detection and recovery mechanisms are performed in local controllers, which may degrade the performance of the local controllers. In controller failure recovery, existing mechanisms did not consider the time-varying load standard deviation metric, which may be used to reduce the flow setup time. To address these problems, we propose a Simulated Annealing-based Efficient Failover (SAEF) mechanism, run as an app in global controllers, to relieve the burden of local controllers for high availability hierarchical SDN controllers. The SAEF uses multiple global controllers to detect a local controller failure and compute a switch migration plan to redo switch-controller association for controller failure recovery. In controller failure detection, global controllers exchange their failure detection results of local controllers to jointly make a local controller failure decision to reduce the mistake rate. In controller failure recovery, the SAEF considers two metrics: switch-controller propagation delay and load standard deviation among local controllers with adaptive weights to adapt to time-varying local controllers' loads. In addition, in our design, a switch is connected to two local controllers so that asynchronous messages, such as packet-in and port-status messages, will not be lost during controller failover. Experiment results using EstiNet show that, the SAEF can achieve efficient failover with the best load balance result in term of load balance metric (LBM) of 1.035, while the best LBM of related works is 1.087. The SAEF also has the lowest flow setup time of 7.837 ms, while the best of related works is 10.418 ms. The lower flow setup time implies that the SDN data plane can receive the response message of a packet-in message faster.