Closer: Scalable Load Balancing Mechanism for Cloud Datacenters

Cloud providers(e.g., Google, Alibaba,Amazon) own large-scale datacenter networks that comprise thousands of switches and links. A loadbalancing mechanism is supposed to effectively utilize the bisection bandwidth. Both Equal-Cost Multi-Path(ECMP), the canonical solution in practice, and alternatives come with performance limitations or significant deployment challenges. In this work, we propose Closer, a scalable load balancing mechanism for cloud datacenters. Closer complies with the evaluation of technology including the deployment of Clos-based topologies, overlays for network virtualization, and virtual machine(VM) clusters. We decouple the system into centralized route calculation and distributed route decision to guarantee its flexibility and stability in large-scale networks. Leveraging In-band Network Telemetry(INT) to obtain precise link state information, a simple but efficient algorithm implements a weighted ECMP at the edge of fabric, which enables Closer to proactively map the flows to the appropriate path and avoid the excessive congestion of a single link. Closer achieves 2 to 7 times better flow completion time(FCT) at 70% network load than existing schemes that work with same hardware environment.