StAN: exploiting shared interests without disclosing them in gossip-based publish/subscribe

Publish/subscribe mechanisms for scalable event dissemination are a core component of many distributed systems ranging from EAI middleware to news dissemination in the Internet. Hence, a lot of research has been done on overlay networks for efficient decentralized topic-based routing. Specifically, in gossip-based dissemination, approximating nodes with shared interests in the overlay makes dissemination more efficient. Unfortunately, this usually requires fully disclosing interests to nearby nodes and impacts reliability due to clustering. In this paper we address this by starting with multiple overlays, one for each topic subscribed, that then separately self-organize to share a large number of physical connections, thereby leading to reduced message traffic and maintenance overhead. This is achieved without a node ever disclosing an interest to another node that doesn’t share it and without impacting the robustness of the overlay. Besides presenting the overlay maintenance protocol, we evaluate it using simulation in order to validate our results

Vitis: A Gossip-based Hybrid Overlay for Internet-scale Publish/Subscribe

Peer-to-peer overlay networks are attractive solutions for building Internet-scale publish/subscribe systems. However, scalability comes with a cost: a message published on a certain topic often needs to traverse a large number of uninterested (unsubscribed) nodes before reaching all its subscribers. This might sharply increase resource consumption for such relay nodes (in terms of bandwidth transmission cost, CPU, etc) and could ultimately lead to rapid deterioration of the system’s performance once the relay nodes start dropping the messages or choose to permanently abandon the system. In this paper, we introduce Vitis, a gossip-based publish/subscribe system that significantly decreases the number of relay messages, and scales to an unbounded number of nodes and topics. This is achieved by the novel approach of enabling rendezvous routing on unstructured overlays. We construct a hybrid system by injecting structure into an otherwise unstructured network. The resulting structure resembles a navigable small-world network, which spans along clusters of nodes that have similar subscriptions. The properties of such an overlay make it an ideal platform for efficient data dissemination in large-scale systems. We perform extensive simulations and evaluate Vitis by comparing its performance against two base-line publish/subscribe systems: one that is oblivious to node subscriptions, and another that exploits the subscription similarities. Our measurements show that Vitis significantly outperforms the base-line solutions on various subscription and churn scenarios, from both synthetic models and real-world traces

Enabling Internet-Scale Publish/Subscribe In Overlay Networks

As the amount of data in todays Internet is growing larger, users are exposed to too much information, which becomes increasingly more difficult to comprehend. Publish/subscribe systems leverage this problem by providing loosely-coupled communications between producers and consumers of data in a network. Data consumers, i.e., subscribers, are provided with a subscription mechanism, to express their interests in a subset of data, in order to be notified only when some data that matches their subscription is generated by the producers, i.e., publishers. Most publish/subscribe systems today, are based on the client/server architectural model. However, to provide the publish/subscribe service in large scale, companies either have to invest huge amount of money for over-provisioning the resources, or are prone to frequent service failures. Peer-to-peer overlay networks are attractive alternative solutions for building Internet-scale publish/subscribe systems. However, scalability comes with a cost: a published message often needs to traverse a large number of uninterested (unsubscribed) nodes before reaching all its subscribers. We refer to this undesirable traffic, as relay overhead. Without careful considerations, the relay overhead might sharply increase resource consumption for the relay nodes (in terms of bandwidth transmission cost, CPU, etc) and could ultimately lead to rapid deterioration of the system’s performance once the relay nodes start dropping the messages or choose to permanently abandon the system. To mitigate this problem, some solutions use unbounded number of connections per node, while some other limit the expressiveness of the subscription scheme. In this thesis work, we introduce two systems called Vitis and Vinifera, for topic-based and content-based publish/subscribe models, respectively. Both these systems are gossip-based and significantly decrease the relay overhead. We utilize novel techniques to cluster together nodes that exhibit similar subscriptions. In the topic-based model, distinct clusters for each topic are constructed, while clusters in the content-based model are fuzzy and do not have explicit boundaries. We augment these clustered overlays by links that facilitate routing in the network. We construct a hybrid system by injecting structure into an otherwise unstructured network. The resulting structures resemble navigable small-world networks, which spans along clusters of nodes that have similar subscriptions. The properties of such overlays make them an ideal platform for efficient data dissemination in large-scale systems. The systems requires only a bounded node degree and as we show, through simulations, they scale well with the number of nodes and subscriptions and remain efficient under highly complex subscription patterns, high publication rates, and even in the presence of failures in the network. We also compare both systems against some state-of-the-art publish/subscribe systems. Our measurements show that both Vitis and Vinifera significantly outperform their counterparts on various subscription and churn scenarios, under both synthetic workloads and real-world traces

Socially aware microcloud service overlay optimization in community networks

Community networks are a growing network cooperation effort by citizens to build and maintain Internet infrastructure in regions that are not available. Adding that, to bring cloud services to community networks (CNs), microclouds were started as an edge cloud computing model where members cooperate using resources. Therefore, enhancing routing for services in CNs is an attractive paradigm that benefits the infrastructure. The problem is the growing consumption of resources for disseminating messages in the CN environment. This is because the services that build their overlay networks are oblivious to the underlying workload patterns that arise from social cooperation in CNs. In this paper, we propose Select in Community Networks (SELECTinCN), which enhances the overlay creation for pub/sub systems over peer-to-peer (P2P) networks. Moreover, SELECTinCN includes social information based on cooperation within CNs by exploiting the social aspects of the community of practice. Our work organizes the peers in a ring topology and provides an adaptive P2P connection establishment algorithm, where each peer identifies the number of connections needed based on the social structure and user availability. This allows us to propagate messages using a reduced number of hops, thus providing an efficient heuristic to an NP-hard problem that maps the workload graph to the structured P2P overlays resulting in a number of messages close to the theoretical minimum. Experiments show that, by using social network information, SELECTinCN reduces the number of relay nodes by up to 89% using the community of practice information versus the state-of-the-art pub/sub notification systems given as baseline.Peer ReviewedPostprint (author's final draft

Design and implementation of an advanced MQTT broker for distributed pub/sub scenarios

MQTT is one of the most popular communication protocols for Internet of Things applications. Based on a publish/subscribe pattern, it relies on a single broker to exchange messages among clients according to topics of interest. However, such a centralized approach does not scale well and is prone to single point of failure risks, calling for solutions where multiple brokers cooperate together in a distributed fashion. In this paper, we present a complete solution for a distributed MQTT broker systems. We target several functional primitives which are key in such a scenario: broker discovery and failure recovery, overlay tree network creation and message routing. Moreover, we also focus on the case where multiple topics are present in the system. In such a scenario, a single tree-based overlay network connecting the different brokers may not be the most efficient solution. To cope with this issue, we propose a topic-based routing scheme for MQTT distributed brokers. The proposed solution creates multiple overlay networks in the distributed system, each one linking together only the brokers whose connected clients have interest in the same topics. We implement the complete system as an extension of the popular HiveMQ MQTT broker and perform several experiments to test its performance in scenarios characterized by a different publishers/subscribers configurations as well as number of topics existing in the system

Middleware for the Internet of Things, Design Goals and Challenges

As the number of wireless devices increases and their size becomes smaller, there can be more interaction between everyday objects of our life. With advances in RFID chips and the introduction of new generations of these devices that are smaller and cheaper, it is possible to put a wireless interface on almost all everyday objects: vehicles, clothes, foodstuffs, etc. This concept is called the \textit{Internet of Things}. Interaction with thousands of wireless devices leads to a continuous and massive flow of events which are generated spontaneously. The question of how to deal with this enormous number of events is challenging and introduces new design goals for a communication mechanism. In this paper we argue that a middleware together with suitable linguistic abstractions is a proper solution. We also point out the challenges in developing this middleware. Moreover, we give an overview of recent related work and describe why they fail to address these challenges

Designing peer-to-peer overlays:a small-world perspective

The Small-World phenomenon, well known under the phrase "six degrees of separation", has been for a long time under the spotlight of investigation. The fact that our social network is closely-knitted and that any two people are linked by a short chain of acquaintances was confirmed by the experimental psychologist Stanley Milgram in the sixties. However, it was only after the seminal work of Jon Kleinberg in 2000 that it was understood not only why such networks exist, but also why it is possible to efficiently navigate in these networks. This proved to be a highly relevant discovery for peer-to-peer systems, since they share many fundamental similarities with the social networks; in particular the fact that the peer-to-peer routing solely relies on local decisions, without the possibility to invoke global knowledge. In this thesis we show how peer-to-peer system designs that are inspired by Small-World principles can address and solve many important problems, such as balancing the peer load, reducing high maintenance cost, or efficiently disseminating data in large-scale systems. We present three peer-to-peer approaches, namely Oscar, Gravity, and Fuzzynet, whose concepts stem from the design of navigable Small-World networks. Firstly, we introduce a novel theoretical model for building peer-to-peer systems which supports skewed node distributions and still preserves all desired properties of Kleinberg's Small-World networks. With such a model we set a reference base for the design of data-oriented peer-to-peer systems which are characterized by non-uniform distribution of keys as well as skewed query or access patterns. Based on this theoretical model we introduce Oscar, an overlay which uses a novel scalable network sampling technique for network construction, for which we provide a rigorous theoretical analysis. The simulations of our system validate the developed theory and evaluate Oscar's performance under typical conditions encountered in real-life large-scale networked systems, including participant heterogeneity, faults, as well as skewed and dynamic load-distributions. Furthermore, we show how by utilizing Small-World properties it is possible to reduce the maintenance cost of most structured overlays by discarding a core network connectivity element – the ring invariant. We argue that reliance on the ring structure is a serious impediment for real life deployment and scalability of structured overlays. We propose an overlay called Fuzzynet, which does not rely on the ring invariant, yet has all the functionalities of structured overlays. Fuzzynet takes the idea of lazy overlay maintenance further by eliminating the need for any explicit connectivity and data maintenance operations, relying merely on the actions performed when new Fuzzynet peers join the network. We show that with a sufficient amount of neighbors, even under high churn, data can be retrieved in Fuzzynet with high probability. Finally, we show how peer-to-peer systems based on the Small-World design and with the capability of supporting non-uniform key distributions can be successfully employed for large-scale data dissemination tasks. We introduce Gravity, a publish/subscribe system capable of building efficient dissemination structures, inducing only minimal dissemination relay overhead. This is achieved through Gravity's property to permit non-uniform peer key distributions which allows the subscribers to be clustered close to each other in the key space where data dissemination is cheap. An extensive experimental study confirms the effectiveness of our system under realistic subscription patterns and shows that Gravity surpasses existing approaches in efficiency by a large margin. With the peer-to-peer systems presented in this thesis we fill an important gap in the family of structured overlays, bringing into life practical systems, which can play a crucial role in enabling data-oriented applications distributed over wide-area networks

WebSocket vs WebRTC in the stream overlays of the Streamr Network

The Streamr Network is a decentralized publish-subscribe system. This thesis experimentally compares WebSocket and WebRTC as transport protocols in the system’s d-regular random graph type unstructured stream overlays. The thesis explores common designs for publish-subscribe and decentralized P2P systems. Underlying network protocols including NAT traversal are explored to understand how the WebSocket and WebRTC protocols function. The requirements set for the Streamr Network and how its design and implementations fulfill them are discussed. The design and implementations are validated with the use simulations, emulations and AWS deployed real-world experiments. The performance metrics measured from the real-world experiments are compared to related work. As the implementations using the two protocols are separate incompatible versions, the differences between them was taken into account during analysis of the experiments. Although the WebSocket versions overlay construction is known to be inefficient and vulnerable to churn, it is found to be unintentionally topology aware. This caused the WebSocket stream overlays to perform better in terms of latency. The WebRTC stream overlays were found to be more predictable and more optimized for small payloads as estimates for message propagation delays had a MEPA of 1.24% compared to WebSocket’s 3.98%. Moreover, the WebRTC version enables P2P connections between hosts behind NATs. As the WebRTC version’s overlay construction is more accurate, reliable, scalable, and churn tolerant, it can be used to create intentionally topology aware stream overlays to fully take over the results of the WebSocket implementation

Building a Framework for High-performance In-memory Message-Oriented Middleware

Message-Oriented Middleware (MOM) is a popular class of software used in many distributed applications, ranging from business systems and social networks to gaming and streaming media services. As workloads continue to grow both in terms of the number of users and the amount of content, modern MOM systems face increasing demands in terms of performance and scalability. Recent advances in networking such as Remote Direct Memory Access (RDMA) offer a more efficient data transfer mechanism compared to traditional kernel-level socket networking used by existing widely-used MOM systems. Unfortunately, RDMA’s complex interface has made it difficult for MOM systems to utilize its capabilities. In this thesis, we introduce a framework called RocketBufs, which provides abstractions and interfaces for constructing high-performance MOM systems. Applications implemented using RocketBufs produce and consume data using regions of memory called buffers while the framework is responsible for transmitting, receiving and synchronizing buffer access. RocketBufs’ buffer abstraction is designed to work efficiently with different transport protocols, allowing messages to be distributed using RDMA or TCP using the same APIs (i.e., by simply changing a configuration file). We demonstrate the utility and evaluate the performance of RocketBufs by using it to implement a publish/subscribe system called RBMQ. We compare it against two widely-used, industry-grade MOM systems, namely RabbitMQ and Redis. Our evaluations show that when using TCP, RBMQ achieves up to 1.9 times higher messaging throughput than RabbitMQ, a message queuing system with an equivalent flow control scheme. When RDMA is used, RBMQ shows significant gains in messaging throughput (up to 3.7 times higher than RabbitMQ and up to 1.7 times higher than Redis), as well as reductions in median delivery latency (up to 81% lower than RabbitMQ and 47% lower than Redis). In addition, on RBMQ subscriber hosts configured to use RDMA, data transfers occur with negligible CPU overhead regardless of the amount of data being transferred. This allows CPU resources to be used for other purposes like processing data. To further demonstrate the flexibility of RocketBufs, we use it to build a live streaming video application by integrating RocketBufs into a web server to receive disseminated video data. When compared with the same application built with Redis, the RocketBufs-based dissemination host achieves live streaming throughput up to 73% higher while disseminating data, and the RocketBufs-based web server shows a reduction of up to 95% in CPU utilization, allowing for up to 55% more concurrent viewers to be serviced