Valerio Schiavoni

A component-based middleware platform for reconfigurable service-oriented architectures

ThetextitService Component Architecture (SCA) is a technology‐independent standard for developing distributed Service‐oriented Architectures (SOA). The SCA standard promotes the use of components and architecture descriptors, and mostly covers the lifecycle steps of implementation and deployment. Unfortunately, SCA does not address the governance of SCA applications and provides no support for the maintenance of deployed components. This article covers this issue and introduces the FRASCATI platform, a run‐time support for SCA with dynamic reconfiguration capabilities and run‐time management features. This article presents the internal component‐based architecture of the FRASCATI platform, and highlights its key features. The component‐based design of the FRASCATI platform introduces many degrees of flexibility and configurability in the platform itself and it can host the SOA applications. This article reports on micro‐benchmarks highlighting that run‐time manageability in the FRASCATI platform does not decrease its performance when compared with the de facto reference SCA implementation: Apache TUSCANY. Finally, a smart home scenario illustrates the extension capabilities and the various reconfigurations of the FRASCATI platform. Copyright

Reconfigurable SCA Applications with the FraSCAti Platform

The Service Component Architecture (SCA) is a technology agnostic standard for developing and deploying distributed service-oriented applications. However, SCA does not define standard means for runtime manageability (including introspection and reconfiguration) of SOA applications and of their supporting environment. This paper presents the FraSCAti platform, which brings runtime management features to SCA, and discusses key principles in its design: the adoption of an extended SCA component model for the implementation of SOA applications and of the FraSCAti platform itself; the use of component-based interception techniques for dynamically weaving non-functional services such as transaction management with components. The paper presents micro-benchmarks that show that runtime manageability in the FraSCAti platform is achieved without hindering its performance relative to the de facto reference SCA implementation, Apaches Tuscany.

NAT-resilient Gossip Peer Sampling

Gossip peer sampling protocols now represent a solid basis to build and maintain peer to peer (p2p) overlay networks. They provide peers with a random sample of the network and maintain connectivity in highly dynamic settings. They rely on the assumption that, at any time, each peer is able to communicate with any other peer. Yet, this ignores the fact that there is a significant proportion of peers that now sit behind NAT devices, preventing direct communication without specific mechanisms. In this paper, we propose a NAT-resilient gossip peer sampling protocol called Nylon, that accounts for the presence of NATs. Nylon is fully decentralized and spreads evenly among peers the extra load caused by the presence of NATs. Nylon ensures that a peer can always communicate with any peer in its sample. This is achieved through a simple, yet efficient mechanism, establishing a path of relays between peers. Our results show that the randomness of the generated samples is preserved, and that the connectivity is not impacted even in the presence of high churn and a high ratio of peers sitting behind NAT devices.

WHISPER: Middleware for Confidential Communication in Large-Scale Networks

A wide range of distributed applications requires some form of confidential communication between groups of users. In particular, the messages exchanged between the users and the identity of group members should not be visible to external observers. Classical approaches to confidential group communication rely upon centralized servers, which limit scalability and represent single points of failure. In this paper, we present WHISPER, a fully decentralized middleware that supports confidential communications within groups of nodes in large-scale systems. It builds upon a peer sampling service that takes into account network limitations such as NAT and firewalls. WHISPER implements confidentiality in two ways: it protects the content of messages exchanged between the members of a group, and it keeps the group memberships secret to external observers. Using multi-hops paths allows these guarantees to hold even if attackers can observe the link between two nodes, or be used as content relays for NAT bypassing. Evaluation in real-world settings indicates that the price of confidentiality remains reasonable in terms of network load and processing costs.

Exploiting Node Connection Regularity for DHT Replication

Distributed Hash-Tables (DHTs) provide an efficient way to store objects in large-scale peer-to-peer systems. To guarantee that objects are reliably stored, DHTs rely on replication. Several replication strategies have been proposed in the last years. The most efficient ones use predictions about the availability of nodes to reduce the number of object migrations that need to be performed: objects are preferably stored on highly available nodes. This paper proposes an alternative replication strategy. Rather than exploiting highly available nodes, we propose to leverage nodes that exhibit regularity in their connection pattern. Roughly speaking, the strategy consists in replicating each object on a set of nodes that is built in such a way that, with high probability, at any time, there are always at least

BRISA: Combining Efficiency and Reliability in Epidemic Data Dissemination

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SPADS: Publisher Anonymization for DHT Storage

nodes in the set that are available. We evaluate this replication strategy using traces of two real-world systems: eDonkey and Skype. The evaluation shows that our regularity-based replication strategy induces a systematically lower network usage than existing state of the art replication strategies.

UniCrawl: A Practical Geographically Distributed Web Crawler

There is an increasing demand for efficient and robust systems able to cope with todays global needs for intensive data dissemination, e.g., media content or news feeds. Unfortunately, traditional approaches tend to focus on one end of the efficiency/robustness design spectrum, by either leveraging rigid structures such as trees to achieve efficient distribution, or using loosely-coupled epidemic protocols to obtain robustness. In this paper we present BRISA, a hybrid approach combining the robustness of epidemic-based dissemination with the efficiency of tree-based structured approaches. This is achieved by having dissemination structures such as trees implicitly emerge from an underlying epidemic substrate by a judicious selection of links. These links are chosen with local knowledge only and in such a way that the completeness of data dissemination is not compromised, i.e., the resulting structure covers all nodes. Failures are treated as an integral part of the system as the dissemination structures can be promptly compensated and repaired thanks to the underlying epidemic substrate. Besides presenting the protocol design, we conduct an extensive evaluation in a real environment, analyzing the effectiveness of the structure creation mechanism and its robustness under faults and churn. Results confirm BRISA as an efficient and robust approach to data dissemination in the large scale.

On the Support of Versioning in Distributed Key-Value Stores

Many distributed applications, such as collaborative Web mapping, collaborative feedback and ranking, or bug reporting systems, rely on the aggregation of privacy-sensitive information gathered from human users. This information is typically aggregated at servers and later used as the basis for some collaborative service. Expecting that clients trust that the user-centric information will not be used for malevolent purposes is not realistic in a fully distributed setting where nodes are not under the control of a single administrative domain. Moreover, most of the time the origin of the data is of small importance when computing the aggregation onto which these services are based. Trust problems can be evinced by ensuring that the identity of the user is dropped before the data can actually be used, a process called publisher anonymization. Such a property shall be guaranteed even if a set of servers is colluding to spy on some user. This also requires that malevolent users cannot harm the service by sending any number of items without being traceable due to publisher anonymization. Rate limitation and decoupled authentication are the two mechanisms that ensure that these cheating users have a limited impact on the system. This paper presents SPADS, a system that interfaces to any DHT and supports the three objectives of publisher anonymization, rate limitation and decoupled authentication. The evaluation of a deployed prototype on a cluster assesses its performance and small footprint.

LAYSTREAM: Composing standard gossip protocols for live video streaming

As the wealth of information available on the web keeps growing, being able to harvest massive amounts of data has become a major challenge. Web crawlers are the core components to retrieve such vast collections of publicly available data. The key limiting factor of any crawler architecture is however its large infrastructure cost. To reduce this cost, and in particular the high upfront investments, we present in this paper a geo-distributed crawler solution, UniCrawl. UniCrawl orchestrates several geographically distributed sites. Each site operates an independent crawler and relies on well-established techniques for fetching and parsing the content of the web. UniCrawl splits the crawled domain space across the sites and federates their storage and computing resources, while minimizing thee inter-site communication cost. To assess our design choices, we evaluate UniCrawl in a controlled environment using the ClueWeb12 dataset, and in the wild when deployed over several remote locations. We conducted several experiments over 3 sites spread across Germany. When compared to a centralized architecture with a crawler simply stretched over several locations, UniCrawl shows a performance improvement of 93.6% in terms of network bandwidth consumption, and a speedup factor of 1.75.