In data centres, efficient initial task placement, and continuous monitoring and migration, is key to maximising resource utilisation, and to minimise task response time.
Task placement and migration must consider both machine resources and application dependencies in order to be efficient. This project develops architectures and mechanisms for providing data-center scalability as a below-layer-4 service. Our tools span from developing multi-objective linear programming models for optimizing task migration, to innovative use of Segment Routing for network-level load balancing.
Cordero, Juan Antonio
On the Dynamics of Single-Orbit Requester-Provider Systems Conference Forthcoming
Proc. 26th ACM International Conference on Modeling, Analysis and Simulation of Wireless and Mobile Systems (MSWiM'2023), ACM, Forthcoming.
This paper considers decentralized systems of multiple agents that interact in order to perform distributed computing or efficient information transfer in variant, constrained environments. These systems appear in various relevant use cases, including reliable multicast distribution, or dynamic resource allocation in systems in the Internet edge (datacenters, IOT deployments). This paper introduces an abstract, mathematical model, that allows to study analytically the behavior of these systems, as a set of interacting requesters and providers. The paper describes system orbits, and concentrates on the study of single-orbit systems. Ergodicity of system behavior in the single-orbit case is proved, and a full description of the stationary system behavior is derived. Closed expressions of the stationary distribution of requester decisions are provided. Analytical results are validated through extensive simulations. These single-orbit results are a necessary step for the analysis and further optimization of dynamic performance of these systems.
Yao, Zhiyuan; Desmouceaux, Yoann; Cordero, Juan Antonio; Townsley, Mark; Clausen, Thomas Heide
In: IEEE Transactions on Network and Service Management, 2022, ISSN: 1932-4537.
In order to dynamically manage and update networking policies in cloud data centers, Virtual Network Functions (VNFs) use, and therefore actively collect, networking state information -and in the process, incur additional control signaling and management overhead, especially in larger data centers. In the meantime, VNFs in production prefer distributed and straightforward heuristics over advanced learning algorithms to avoid intractable additional processing latency under high-performance and low-latency networking constraints. This paper identifies the challenges of deploying learning algorithms in the context of cloud data centers, and proposes Aquarius to bridge the application of machine learning (ML) techniques on distributed systems and service management. Aquarius passively yet efficiently gathers reliable observations, and enables the use of ML techniques to collect, infer, and supply accurate networking state information -without incurring additional signaling and management overhead. It offers fine-grained and programmable visibility to distributed VNFs, and enables both open-and close-loop control over networking systems. This paper illustrates the use of Aquarius with a traffic classifier, an auto-scaling system, and a load balancer -and demonstrates the use of three different ML paradigms -unsupervised, supervised, and reinforcement learning, within Aquarius, for network state inference and service management. Testbed evaluations show that Aquarius suitably improves network state visibility and brings notable performance gains for various scenarios with low overhead.
Yao, Zhiyuan; Ding, Zihan
In: 36th Conference on Neural Information Processing Systems (NeurIPS 2022), 2022.
This paper investigates the network load balancing problem in data centers (DCs) where multiple load balancers (LBs) are deployed, using the multi-agent reinforcement learning (MARL) framework. The challenges of this problem consist of the heterogeneous processing architecture and dynamic environments, as well as limited and partial observability of each LB agent in distributed networking systems, which can largely degrade the performance of in-production load balancing algorithms in real-world setups. Centralised-training-decentralised-execution (CTDE) RL scheme has been proposed to improve MARL performance, yet it incurs -- especially in distributed networking systems, which prefer distributed and plug-and-play design scheme -- additional communication and management overhead among agents. We formulate the multi-agent load balancing problem as a Markov potential game, with a carefully and properly designed workload distribution fairness as the potential function. A fully distributed MARL algorithm is proposed to approximate the Nash equilibrium of the game. Experimental evaluations involve both an event-driven simulator and real-world system, where the proposed MARL load balancing algorithm shows close-to-optimal performance in simulations, and superior results over in-production LBs in the real-world system.
Yao, Zhiyuan; Desmouceaux, Yoann; Cordero, Juan Antonio; Townsley, Mark; Clausen, Thomas Heide
Efficient Data-Driven Network Functions Proceedings Article
In: 30th International Symposium on the Modeling, Analysis, and Simulation of Computer and Telecommunication Systems (MASCOTS 2022), 2022.
Cloud environments require dynamic and adaptive networking policies. It is preferred to use heuristics over advanced learning algorithms in Virtual Network Functions (VNFs) in production becuase of high-performance constraints. This paper proposes Aquarius to passively yet efficiently gather observations and enable the use of machine learning to collect, infer, and supply accurate networking state information-without incurring additional signalling and management overhead. This paper illustrates the use of Aquarius with a traffic classifier, an autoscaling system, and a load balancer-and demonstrates the use of three different machine learning paradigms-unsupervised, supervised, and reinforcement learning, within Aquarius, for inferring network state. Testbed evaluations show that Aquarius increases network state visibility and brings notable performance gains with low overhead.
Yao, Zhiyuan; Ding, Zihan; Clausen, Thomas Heide
Multi-agent reinforcement learning for network load balancing in data center Proceedings Article
In: 31st ACM International Conference on Information and Knowledge Management (CIKM'22), 2022.
This paper presents the network load balancing problem, a challenging real-world task for multi-agent reinforcement learning (MARL) methods. Conventional heuristic solutions like Weighted-Cost Multi-Path (WCMP) and Local Shortest Queue (LSQ) are less flexible to the changing workload distributions and arrival rates, with a poor balance among multiple load balancers. The cooperative network load balancing task is formulated as a Dec-POMDP problem, which naturally induces the MARL methods. To bridge the reality gap for applying learning-based methods, all models are directly trained and evaluated on a real-world system from moderate- to large-scale setups. Experimental evaluations show that the independent and “selfish” load balancing strategies are not necessarily the globally optimal ones, while the proposed MARL solution has a superior performance over different realistic settings. Additionally, the potential difficulties of the application and deployment of MARL methods for network load balancing are analysed, which helps draw the attention of the learning and network communities to such challenges.
Yao, Zhiyuan; Desmouceaux, Yoann; Cordero, Juan Antonio; Clausen, Thomas Heide
HLB: Towards Load-Aware Load-Balancing Journal Article
In: IEEE/ACM Transactions on Networking, 2022, ISSN: 1558-2566.
The purpose of network load balancers is to optimize quality of service to the users of a set of servers - basically, to improve response times and to reducing computing resources - by properly distributing workloads. This paper proposes a distributed, application-agnostic, Hybrid Load Balancer (HLB) that - without explicit monitoring or signaling - infers server occupancies and processing speeds, which allows making optimised workload placement decisions. This approach is evaluated both through simulations and extensive experiments, including synthetic workloads and Wikipedia replays on a real-world testbed. Results show significant performance gains, in terms of both response time and system utilisation, when compared to existing load-balancing algorithms.
Yao, Zhiyuan; Ding, Zihan; Clausen, Thomas Heide
Reinforced Workload Distribution Fairness Proceedings Article
In: Machine Learning for Systems at 35th Conference on Neural Information Processing Systems (NeurIPS 2021), 2021.
Network load balancers are central components in data centers, that distributes workloads across multiple servers and thereby contribute to offering scalable services. However, when load balancers operate in dynamic environments with limited monitoring of application server loads, they rely on heuristic algorithms that require manual configurations for fairness and performance. To alleviate that, this paper proposes a distributed asynchronous reinforcement learning mechanism to-with no active load balancer state monitoring and limited network observations-improve the fairness of the workload distribution achieved by a load balancer. The performance of proposed mechanism is evaluated and compared with stateof-the-art load balancing algorithms in a simulator, under configurations with progressively increasing complexities. Preliminary results show promise in RLbased load balancing algorithms, and identify additional challenges and future research directions, including reward function design and model scalability.
Yao, Zhiyuan; Desmouceaux, Yoann; Townsley, Mark; Clausen, Thomas Heide
Towards Intelligent Load Balancing in Data Centers Proceedings Article
In: Machine Learning for Systems at 35th Conference on Neural Information Processing Systems (NeurIPS 2021), Dec 2021, Sydney, Australia, 2021.
Network load balancers are important components in data centers to provide scalable services. Workload distribution algorithms are based on heuristics, e.g., Equal-Cost Multi-Path (ECMP), Weighted-Cost Multi-Path (WCMP) or naive machine learning (ML) algorithms, e.g., ridge regression. Advanced ML-based approaches help achieve performance gain in different networking and system problems. However, it is challenging to apply ML algorithms on networking problems in real-life systems. It requires domain knowledge to collect features from low-latency, high-throughput, and scalable networking systems, which are dynamic and heterogenous. This paper proposes Aquarius to bridge the gap between ML and networking systems and demonstrates its usage in the context of network load balancers. This paper demonstrates its ability of conducting both offline data analysis and online model deployment in realistic systems. The results show that the ML model trained and deployed using Aquarius improves load balancing performance yet they also reveals more challenges to be resolved to apply ML for networking systems.
Rizzi, Carmine; Yao, Zhiyuan; Desmouceaux, Yoann; Townsley, Mark; Clausen, Thomas Heide
Charon: Load-Aware Load-Balancing in P4 Proceedings Article
In: 1st Joint International Workshop on Network Programmability & Automation (NetPA) at 17th International Conference on Network and Service Management (CNSM 2021),, 2021.
Load-Balancers play an important role in data centers as they distribute network flows across application servers and guarantee per-connection consistency. It is hard however to make fair load balancing decisions so that all resources are efficiently occupied yet not overloaded. Tracking connection states allows to infer server load states and make informed decisions, but at the cost of additional memory space consumption. This makes it hard to implement on programmable hardware, which has constrained memory but offers line-rate performance. This paper presents Charon, a stateless load-aware load balancer that has line-rate performance implemented in P4-NetFPGA. Charon passively collects load states from application servers and employs the power-of-2-choices scheme to make data-driven load balancing decisions and improve resource utilization. Perconnection consistency is preserved statelessly by encoding server ID in a covert channel. The prototype design and implementation details are described in this paper. Simulation results show performance gains in terms of load distribution fairness, quality of service, throughput and processing latency.
Hawari, Mohammed; Clausen, Thomas
OP4T: Bringing Advanced Network Packet Timestamping into the Field Proceedings Article
In: 2021 International Conference on Information Networking (ICOIN), pp. 137-142, 2021.
Because it is very bursty, the microsecond-scale temporal behaviour of network traffic in data-centres is chal- lenging to measure and understand. To bring observability into data-centre networks, this paper introduces the Open Platform for Programmable Precise Packet Timestamping (OP4T), a hardware architecture, targeting Field-Programmable Gateway Arrays (FPGAs), integrated into data-centre servers as a Smart Network Interface Card (SmartNIC), and flexible enough to enable advanced latency diagnosis.
In this paper, OP4T is specified, and an open-source im- plementation of that architecture is proposed, targeting the NetFPGA SUME prototyping board. By leveraging the P4 programming language, and partial reconfiguration, that open- source implementation is experimentally shown to enable in-band, precise packet timestamping, without sacrificing the achievable throughput. As an illustration, OP4T is shown to be usable to measure fine-grained properties of a software packet forwarder, e.g., packet batching.
Hawari, Mohammed; Cordero, Juan Antonio; Clausen, Thomas
In: IEEE/ACM Transactions on Networking, pp. 1-15, 2020, ISSN: 1558-2566.
This addresses the problem of high-quality packet pacing for constant-rate packet consumption systems, with strict buffering limitations. A mostly-software pacing architecture is developed, which has minimal hardware requirements, satisfied by commodity servers - rendering the proposed solution easily deployable in existing (data-centre) infrastructures. Two algorithms (free-running and frequency-controlled pacing, for explicitly and implicitly indicated target rates, respectively) are specified, and formally analysed. The proposed solution, including both algorithms, is implemented, and is tested on real hardware and under real conditions. The performance of these implementations is experimentally evaluated and compared to existing mechanisms, available in general-purpose hardware. Results of both exhaustive experiments, and of an analytical modeling, indicate that the proposed approach is able to perform low-jitter packet pacing on commodity hardware, being thus suitable for constant rate transmission and consumption in media production scenarios.
Desmouceaux, Yoann; Toubaline, Sonia; Clausen, Thomas
Flow-Aware Workload Migration in Data Centers Journal Article
In: Springer - Journal of Network and Systems Management (JONS), 2018.
In data centers, subject to workloads with heterogeneous (and sometimes short) lifetimes, workload migration is a way of attaining a more efficient utilization of the underlying physical machines.
To not introduce performance degradation, such workload migration must take into account not only machine resources, and per-task resource requirements, but also application dependencies in terms of network communication.
This articleformat presents a workload migration model capturing all of these constraints.
A linear programming framework is developed allowing accurate representation of per-task resources requirements and inter-task network demands. Using this, a multi-objective problem is formulated to compute a re-allocation of tasks that (i) maximizes the total inter-task throughput, while (ii) minimizing the cost incurred by migration and (iii) allocating the maximum number of new tasks.
A baseline algorithm, solving this multi-objective problem using the $epsilon$-constraint method is proposed, in order to generate the set of Pareto-optimal solutions. As this algorithm is compute-intensive for large topologies, a heuristic, which computes an approximation of the Pareto front, is then developed, and evaluated on different topologies and with different machine load factors. These evaluations show that the heuristic can provide close-to-optimal solutions, while reducing the solving time by one to two order of magnitudes.
Desmouceaux, Yoann; Pfister, Pierre; Tollet, Jérôme; Townsley, W. Mark; Clausen, Thomas
In: IEEE/ACM Transactions on Networking, vol. 26, no. 2, pp. 819-834, 2018, ISSN: 1063-6692.
Network load-balancers generally either do not take application state into account, or do so at the cost of a central- ized monitoring system. This paper introduces a load-balancer running exclusively within the IP forwarding plane, i.e. in an application protocol agnostic fashion – yet which still provides application-awareness and makes real-time, decentralized deci- sions. To that end, IPv6 Segment Routing is used to direct data packets from a new flow through a chain of candidate servers, until one decides to accept the connection, based solely on its local state. This way, applications themselves naturally decide on how to fairly share incoming connections, while incurring minimal network overhead, and no out-of-band signaling. A consistent hashing algorithm, as well as an in-band stickiness protocol, allow for the proposed solution to be able to be reliably distributed across a large number of instances.
Performance evaluation by means of an analytical model and actual tests on different workloads (including a Wikipedia replay as a realistic workload) show significant performance benefits in terms of shorter response times, when compared to a traditional random load-balancer. In addition, this paper introduces and compares kernel bypass high-performance implementations of both 6LB and a state-of-the-art load-balancer, showing that the significant system-level benefits of 6LB are achievable with a negligible data-path CPU overhead.
Desmouceaux, Yoann; Pfister, Pierre; Tollet, Jerome; Townsley, W. Mark; Clausen, Thomas
SRLB: The Power of Choices in Load Balancing with Segment Routing Proceedings Article
In: In Proceedings of the 37th IEEE International Conference on Distributed Computing Systems (ICDCS), 2017.
Network load-balancers generally either do not take application state into account, or do so at the cost of a central- ized monitoring system. This paper introduces a load-balancer running exclusively within the IP forwarding plane, i.e. in an application protocol agnostic fashion – yet which still provides application-awareness and makes real-time, decentralized deci- sions. To that end, IPv6 Segment Routing is used to direct data packets from a new flow through a chain of candidate servers, until one decides to accept the connection, based on its local state. This way, applications themselves naturally decide on how to share incoming connections, while incurring minimal network overhead, and no out-of-band signaling.
Tests on different workloads – including realistic workloads such as replaying actual Wikipedia access traffic towards a set of replica Wikipedia instances – show significant performance benefits, in terms of shorter response times, when compared to a traditional random load-balancer.