Stable and Fault-Tolerant Decentralized Traffic Engineering

2025-10-13

AI Summary

In decentralized traffic engineering for cloud-wide area networks, distributed slice controllers independently optimize traffic allocation, often leading to conflicting decisions and link overloads (up to 30% above capacity). To address this, we propose a regularized cooperative control framework: (i) a quadratic regularization term is introduced into the distributed optimization objective to enhance convergence stability, enabling slice controllers to reach globally compatible solutions without explicit coordination; and (ii) a randomized network slicing algorithm is designed to optimize critical traffic distribution and significantly reduce the impact domain of single-point failures. End-to-end evaluation on a production cloud network demonstrates that our approach reduces congestion events caused by decision conflicts by 14× and shrinks the fault impact radius by 79%, achieving both high availability and traffic stability.

Technology Category

• Search and Optimization: Distributed Search
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems

Application Category

• Responsible Web: Human-perceived consequences of algorithmic deployment on the web
• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• Economics, Online Markets and Human Computation: Incentives in network design for Web infrastructures and ecosystems

Abstract

Cloud providers have recently decentralized their wide-area network traffic engineering (TE) systems to contain the impact of TE controller failures. In the decentralized design, a controller fault only impacts its slice of the network, limiting the blast radius to a fraction of the network. However, we find that autonomous slice controllers can arrive at divergent traffic allocations that overload links by 30% beyond their capacity. We present Symphony, a decentralized TE system that addresses the challenge of divergence-induced congestion while preserving the fault-isolation benefits of decentralization. By augmenting TE objectives with quadratic regularization, Symphony makes traffic allocations robust to demand perturbations, ensuring TE controllers naturally converge to compatible allocations without coordination. In parallel, Symphony's randomized slicing algorithm partitions the network to minimize blast radius by distributing critical traffic sources across slices, preventing any single failure from becoming catastrophic. These innovations work in tandem: regularization ensures algorithmic stability to traffic allocations while intelligent slicing provides architectural resilience in the network. Through extensive evaluation on cloud provider WANs, we show Symphony reduces divergence-induced congestion by 14x and blast radius by 79% compared to current practice.

Problem

• Preventing link overload from divergent traffic allocations
• Maintaining fault isolation in decentralized network systems
• Ensuring algorithmic stability and architectural resilience simultaneously

Innovation

• Quadratic regularization ensures robust traffic allocations
• Randomized slicing minimizes failure impact across network
• Combined algorithmic stability and architectural resilience enhancement