Lazy Ctrl: Scalable Network Control for Cloud Data Centers

The advent of software defined networking enables flexible, reliable and feature-rich control planes for data center networks. However, the tight coupling of centralized control and complete visibility leads to a wide range of issues among which scalability has risen to prominence. We observe that data center traffic is usually highly skewed and thus edge switches can be grouped according to traffic locality. As a result, the workload of the central controller could be highly reduced if we carry out distributed control inside those groups. Based on the above observation, we present LazyCtrl, a novel hybrid control plane design for data center networks. LazyCtrl aims at bringing laziness to the central controller by dynamically devolving most of the control tasks to independent switch groups to process frequent intra-group events using distributed control mechanisms, while handling rare inter-group or other specified events by the controller. We implement LazyCtrl and build a prototype based on Open vSwich and Floodlight. Trace-driven experiments on our prototype show that an effective switch grouping is easy to maintain in multi-tenant clouds and the central controller can be significantly shielded by staying lazy, with its workload reduced by up to 82%.