A Distributed Presence Service over Epidemic Multicast

In a dynamic distributed system with a very large number of nodes, such as a cloud, it issometimes useful to discover the nodes that are up in the system at a given time. The number of those nodes changes continually along the operation time, as some nodes crash and some join the system. In this paper we introduce a presence service that was implemented over a gossip structure using an epidemic multicast protocol. Unlike other common presence services, our service is fully distributed. Due to epidemic dissemination and inherent redundancy provided by the multicast protocol, the service is resilient against message loss and link crashes. In a scenario we developed to evaluate the efficiency and scalability of our presence service, we show how presence notifications propagate to reach all nodes in the group and we also show how adjustments for the gossip configuration can benefit the efficiency and resilience of the notification dissemination. The results of the experimental evaluation show that following a distributed approach over epidemic communication leads to a resilient and scalable presence service.Key words: Presence service, epidemic protocols, resilience, fault tolerance, clouds

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

Compositional gossip: a conceptual architecture for designing gossip-based applications

Most proposed gossip-based systems use an ad-hoc design. We observe a low degree of reutilization among this proposals. We present how this limits both the systematic development of gossip-based applications and the number of applications that can benefit from gossip-based construction. We posit that these reinvent-the-wheel approaches poses a significant barrier to the spread and usability of gossip protocols. This paper advocates a conceptual design framework based upon aggregating basic and predefined building blocks BD 2. We show how to compose building blocks within our framework to construct more complex blocks to be used in gossip-based applications. The concept is further depicted with two gossip-based applications described using our building blocks.(undefined

LHView: Location Aware Hybrid Partial View

The rise of the Cloud creates enormous business opportunities for companies to provide global services, which requires applications supporting the operation of those services to scale while minimizing maintenance costs, either due to unnecessary allocation of resources or due to excessive human supervision and administration. Solutions designed to support such systems have tackled fundamental challenges from individual component failure to transient network partitions. A fundamental aspect that all scalable large systems have to deal with is the membership of the system, i.e, tracking the active components that compose the system. Most systems rely on membership management protocols that operate at the application level, many times exposing the interface of a logical overlay network, that should guarantee high scalability, efficiency, and robustness. Although these protocols are capable of repairing the overlay in face of large numbers of individual components faults, when scaling to global settings (i.e, geo-distributed scenarios), this robustness is a double edged-sword because it is extremely complex for a node in a system to distinguish between a set of simultaneously node failures and a (transient) network partition. Thus the occurrence of a network partition creates isolated sub-sets of nodes incapable of reconnecting even after the recovery from the partition. This work address this challenges by proposing a novel datacenter-aware membership protocol to tolerate network partitions by applying existing overlay management techniques and classification techniques that may allow the system to efficiently cope with such events without compromising the remaining properties of the overlay network. Furthermore, we strive to achieve these goals with a solution that requires minimal human intervention

Resource discovery for distributed computing systems: A comprehensive survey

Large-scale distributed computing environments provide a vast amount of heterogeneous computing resources from different sources for resource sharing and distributed computing. Discovering appropriate resources in such environments is a challenge which involves several different subjects. In this paper, we provide an investigation on the current state of resource discovery protocols, mechanisms, and platforms for large-scale distributed environments, focusing on the design aspects. We classify all related aspects, general steps, and requirements to construct a novel resource discovery solution in three categories consisting of structures, methods, and issues. Accordingly, we review the literature, analyzing various aspects for each category

Luotettavuuden ja toisteisuuden toteutus aikakriittiseen televiestintäjärjestelmään

Different distributed systems have different requirements for reliability. One way for increasing reliability is fault tolerance. Methods for increasing fault tolerance have been studied for decades, starting from early hardware level fault tolerance until more recent studies for peer-to-peer and cloud computing fault tolerance. In this paper, fault tolerance of an existing telecommunication service platform is studied and improved. Even in the case of a failure of a single server, called a call handler, any data should not be lost. Three sub-problems with different expectations are presented: failure detection, data dissemination and takeover. The implemented failure detection protocol is based on a basic gossip-style heartbeat protocol. The data dissemination protocol is a gossip-style dissemination protocol which, unlike traditional gossip algorithms, does not select its targets fully randomly. Instead, known data about which call handlers have received and might have received a message are used when selecting targets. On top of both, a simple takeover protocol is implemented. Testing was done in a closed environment both for the failure detection and for the data dissemination, as well as for whole the system. The results show that failure detection protocol is able to provide adequate detection times and accuracy. The nature of the implemented data dissemination algorithm is very spamming by the results. The amount of sent messages can, however, be greatly decreased with design decisions. Test results for whole the system indicate that the system is able to provide over 99 % reliability even with large server crash probabilities at least up to call handler amount 16. Unfortunately, resources in the testing environment were limited and that is why memory problems started to occur affecting the test results starting from 17 call handlers. That is why larger call handler amounts could not be tested.Erilaisilla hajautetuilla järjestelmillä on eri vaatimuksia luotettavuudelle. Eräs tapa parantaa luotettavuutta on vikasietoisuuden kasvattaminen. Erilaisia tapoja parantaa vikasietoisuutta on tutkittu jo vuosikymmeniä. Aikaisimmat tutkimukset keskittyivät pääasiallisesti laitteistotason vikasietoisuuteen, mutta viime aikoina päämielenkiinnonkohde on siirtynyt vertaisverkkojen ja pilviteknologioiden vikasietoisuuden tutkimiseen. Tämän opinnäytetyön tarkoituksena on tutkia ja parantaa olemassaolevan televiestintäjärjestelmän luotettavuutta vikasietoisuudella. Päämääränä on toteuttaa ratkaisu, joka pitää huolta ettei tietoa katoa puhelunkäsittelijöiden vikatilanteissa. Varsinainen ongelma on jaettu osa-alueisiin: virheen havaitsemiseen, tiedon levittämiseen ja haltuunottoon. Virheenhavaitsemisprotokolla pohjautuu juorutyyliseen sydämenlyöntiprotokollaan. Tiedon levittäminen on toteutettu juorutyylisellä tiedonlevitysprotokollalla, joka ei valitse lähetyskohteitaan täysin satunnaisesti, toisin kuin perinteinen juoruprotokolla. Sen sijaan valinnassa käytetään hyväksi tietoa verkon jäsenistä, jotka ovat jo vastaanottaneet viestin tai ovat mahdollisesti vastaanottaneet viestin. Puheluiden haltuunottoprotokolla on toteutettu hyödyntäen edellisiä protokollia. Testaus toteutettiin suljetussa ympäristössä. Erilliset testit suoritettiin virheenhavaitsemis- ja tiedon levittämisprotokollille. Lisäksi tehtiin koko järjestelmätason testejä. Virheenhavaitsemisprotokolla näyttää tulosten perusteella tarjoavan riittävän hyvän havaitsemisajan ja -tarkkuuden. Tulosten perusteella tiedonlevittämisprotokolla luo paljon viestejä, mutta viestimääriin pystyy vaikuttamaan protokollasuunnittelulla. Koko järjestelmän testit viittaisivat siihen, että yli 99 % luotettavuus saavutetaan jopa suurilla kaatumistodennäköisyyksillä ainakin 16 puhelunkäsittelijään asti. Testiympäristön resurssit olivat rajoitetut, mistä johtuen jo 17 puhelunkäsittelijän testeissä esiintyi muistiongelmia, jotka vaikuttivat tuloksiin. Suurempia jäsenmääriä ei siksi pystytty testaamaan

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

Scalability approaches for causal multicast: a survey

The final publication is available at Springer via http://dx.doi.org/10.1007/s00607-015-0479-0Many distributed services need to be scalable: internet search, electronic commerce, e-government... In order to achieve scalability, high availability and fault tolerance, such applications rely on replicated components. Because of the dynamics of growth and volatility of customer markets, applications need to be hosted by adaptive, highly scalable systems. In particular, the scalability of the reliable multicast mechanisms used for supporting the consistency of replicas is of crucial importance. Reliable multicast might propagate updates in a pre-determined order (e.g., FIFO, total or causal). Since total order needs more communication rounds than causal order, the latter appears to be the preferable candidate for achieving multicast scalability, although the consistency guarantees based on causal order are weaker than those of total order. 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A decentralized framework for cross administrative domain data sharing

Federation of messaging and storage platforms located in remote datacenters is an essential functionality to share data among geographically distributed platforms. When systems are administered by the same owner data replication reduces data access latency bringing data closer to applications and enables fault tolerance to face disaster recovery of an entire location. When storage platforms are administered by different owners data replication across different administrative domains is essential for enterprise application data integration. Contents and services managed by different software platforms need to be integrated to provide richer contents and services. Clients may need to share subsets of data in order to enable collaborative analysis and service integration. Platforms usually include proprietary federation functionalities and specific APIs to let external software and platforms access their internal data. These different techniques may not be applicable to all environments and networks due to security and technological restrictions. Moreover the federation of dispersed nodes under a decentralized administration scheme is still a research issue. This thesis is a contribution along this research direction as it introduces and describes a framework, called \u201cWideGroups\u201d, directed towards the creation and the management of an automatic federation and integration of widely dispersed platform nodes. It is based on groups to exchange messages among distributed applications located in different remote datacenters. Groups are created and managed using client side programmatic configuration without touching servers. WideGroups enables the extension of the software platform services to nodes belonging to different administrative domains in a wide area network environment. It lets different nodes form ad-hoc overlay networks on-the-fly depending on message destinations located in distinct administrative domains. It supports multiple dynamic overlay networks based on message groups, dynamic discovery of nodes and automatic setup of overlay networks among nodes with no server-side configuration. I designed and implemented platform connectors to integrate the framework as the federation module of Message Oriented Middleware and Key Value Store platforms, which are among the most widespread paradigms supporting data sharing in distributed systems