Self-Management – Potentiale, Probleme, Perspektiven

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Gordon Moores Gesetz vom exponentiellen Wachstum der Transistordichte pro Quadrat-Zoll hat seit 1965 die IT-Industrie geprägt. Mit der damit einhergehenden Explosion der Rechnerleistung wurde die Software immer leistungsfähiger, und man ist dazu übergegangen, Rechnersysteme zu vernetzen und Anwendungen zu verteilen. Eine Folge dieser Entwicklungen ist die rapide zunehmende Komplexität der modernen Informationstechnologie. 40 Jahre nach Moores Entdeckung droht eben diese Tatsache, dem bisherigen exponentiellen Wachstum natürliche Grenzen zu setzen. Moderne, vernetzte Rechnersysteme, wie sie in der Industrie weit verbreitet sind, sind schon heute zu komplex als dass sie auf manuellem Wege, d.h., durch menschliche Administratoren, in einem optimalen Betriebszustand gehalten werden können. Die Folgen sind eine unzureichende Ausnutzung vorhandener Ressourcen, wiederkehrende Fehlerzustände und Lücken in der Absicherung gegen mutwillige Angriffe auf die System-Integrität. Dies führt zu erheblichen finanziellen Mehraufwendungen bzw. Verlusten. Ein permanent überfordertes Administrationspersonal, trägt durch eigene Fehler ein Übriges bei.Schenkt man den jüngst aufkeimenden Initiativen von IT-Giganten wie IBM, Microsoft und Sun Glauben, so heißt die Lösung dieser Misere automatisiertes Management. Vernetzte Rechnersysteme sollen sich auf lange Sicht selbst verwalten. Man erhofft sich hiervon ein effektiveres Management und eine Freistellung von Personal, welches sich dann um wichtigere Aufgaben kümmern kann.In diesem Beitrag beleuchten wir den aktuellen Stand und die Perspektiven im Bereich des Self-Managements. Des Weiteren diskutieren wir offene Fragen, welche auf dem Weg zu selbstverwaltenden Systemen zu lösen sind

Content-based Publish/Subscribe in Software-defined Networks

With SDN, content-based publish/subscribe can be implemented on the network layer instead of using an application layer broker network. We present two methods realizing notification distribution with OpenFlow and P4, respectively

Towards Energy-Aware Multi-Core Scheduling

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.There are two major current trends that can easily be identified in computer industry: (i) the shift towards massively parallelization fostered by multi-core technology resulting in growing numbers of cores per processor and (ii) the increasing importance of energy-awareness in computing due to rising energy costs and environmental awareness. In current operating systems, these two issues are often addressed independently: one component, the scheduler, assigns processes to cores and a second component manages the power states of individual cores in time. In this paper, we explain why this orthogonal treatment can lead to problems such as a considerably degraded system performance in case of on-demand processor power state management. Furthermore, we present an approach to energy-aware multi-core scheduling at the operating system level avoiding the performance penalty while still saving energy. To corroborate our argumentation and to illustrate the applicability of the presented approach, we give numbers from experiments based on Linux and current multi-core processors

Realtime Publish/Subscribe for the Industrial Internet of Things

Publish/subscribe communication offers outstanding flexibility, but lacks the predictability required for guaranteeing (hard) realtime constraints in industrial environments such as future smart factories. In this paper, we review existing publish/ subscribe systems, identify their shortcomings, and derive research objectives for a converged realtime network infrastructure for the Industrial Internet of Things (IIoT) that is based on publish/subscribe and Software-Defined Networking (SDN)

P4-programmable Data Plane for Content-based Publish/Subscribe

The domain-specific programming language P4 enables developers to specify how data plane devices (e.g., switches, routers) process packets. This opens up novel opportunities for efficient information dissemination at the network layer drastically reducing notification delays compared to applicationlayer publish/subscribe using broker overlay networks. In this paper, we present three different strategies that use P4 to realize content-based publish/subscribe. We start with a source routing strategy that is, then, improved to exploit and adapt a preinstalled forwarding tree by adding or removing branches if required. The most advanced strategy enables multiple forwarding trees to be dynamically stitched and adapted as needed

Fast Publish/Subscribe Using Linux eBPF

In recent years, the requirements for publish/subscribe systems have changed enormously. Mainly, this is due to the vastly increasing number of smart objects, services, and apps being connected to the cloud and their growing demand for bandwidth and realtime message processing. Unfortunately, many publish/subscribe systems are hardly able to handle both necessary and available data rates when being built on conventional network stacks that suffer from significant system overhead. In this paper, we present a novel architecture for fast publish/subscribe that consists of an edge broker for preprocessing notifications and a cloud broker that leverages eBPF to efficiently process network packages and speed up notification delivery. We address limitations of eBPF, discuss different filter options, and quantify the achievable performance. The evaluation confirms a significant performance improvement of the eBPF-enabled cloud broker when compared to a conventional implementation

Autonomie in IT-Systemen : Ein Konzeptionelles Modell

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Die Erforschung und Anwendung von autonomen Systemen ist momentan in der Informatik ein Themengebiet von wachsendem Interesse. Die Aussicht, mit autonomen Verfahren komplexe Systeme handhabbar zu machen und Kosteneinsparungen bei deren Betrieb zu erzielen, hat bereits die Softwareindustrie auf dieses Thema gelenkt und zu neuartigen Produkten geführt. Andererseits darf die Verlässlichkeit eines Systems nicht aufgrund eines autonomen Verfahrens herabgesetzt werden. Dieses Spannungsfeld ist ein Fokus verschiedener Forschungsbemühungen, um autonome Systeme alltagstauglich zu machen.Beim Gebiet der autonomen Systeme handelt es sich um ein junges Themengebiet, welches noch nicht durch allgemein akzeptierte Definitionen geprägt ist. Dadurch entsteht der Bedarf einer terminologischen Basis, die sich momentan in der Phase der Etablierung befindet. Diese Arbeit beteiligt sich an diesem Prozess und schlägt ein konzeptionelles Modell vor. Dieses Modell benennt die grundlegenden Termini und zeigt deren Zusammenhänge auf. Es beschreibt eine Interpretation der relevanten Begriffe und leitet daraus Relationen ab. Auf diese Weise fördert es das gemeinsame Verständnis und erleichtert die Kommunikation bezüglich spezifischer Fragestellungen innerhalb dieses Gebietes

A Simulation Model for Investigating Clock Synchronization Issues in Time-Sensitive Networks

The IEEE 802.1 Time-Sensitive Networking (TSN) task force has set guidelines for IEEE 802.3 networks allowing deterministic realtime communication over Ethernet. To execute deterministic time-triggered scheduling operations, the network nodes need to be synchronized. One application of time synchronization is distributed data acquisition for the Wendelstein 7-X nuclear fusion experiment. Both the system control and the scientific evaluation of the experiments need measurement timestamps with accuracies in the nanosecond range. The TSN standard IEEE 802.1AS has specified the generalized Precision Time Protocol (gPTP) which executes the synchronization process. However, there are some issues that are not addressed in the standard such as the impact of clock skew and drift of network nodes on the number of resynchronizations needed to maintain the required synchronization accuracy. This paper introduces an OMNeT++ simulation model, which can be used to investigate clock synchronization issues in time-sensitive networks

Large-Scale Content-Based Publish-Subscribe Systems

Today, the architecture of distributed computer systems is dominated by client/server platforms relying on synchronous request/reply. This architecture is not well suited to implement information-driven applications like news delivery, stock quoting, air traffic control, and dissemination of auction bids due to the inherent mismatch between the demands of these applications and the characteristics of those platforms. In contrast to that, publish/subscribe directly reflects the intrinsic behavior of information-driven applications because communication here is indirect and initiated by producers of information: Producers publish notifications and these are delivered to subscribed consumers by the help of a notification service that decouples the producers and the consumers. Therefore, publish/subscribe should be the first choice for implementing such applications. The expressiveness of the notification selection mechanism used by the consumers to describe the notifications they are interested in is crucial for the flexibility of a notification service. Content-based notification selection is most expressive because it allows to evaluate filter predicates over the whole content of a notification. The advantage in expressiveness compared to channel- or subject-based selection results in increased flexibility facilitating extensibility and change. On the other hand, scalable implementations of content-based notification services are difficult to realize. Indeed, the expressiveness of notification selection must be carefully chosen in large-scale systems, because expressiveness and scalability are interdependent. Hence, the most fundamental problem in the area of content-based publish/subscribe systems is probably the scalable routing of notifications from their producers to their respective consumers. Unfortunately, existing content-based notification services are not mature enough to be used in large-scale, widely-distributed environments. Most existing notification services are either centralized, use flooding, or use simple routing algorithms that assume that each event broker has global knowledge about all active subscriptions. All these approaches exhibit severe scalability problems in large-scale systems. In contrast to that, this thesis concentrates on mechanisms to improve the scalability of content-based routing algorithms and presents more advanced routing algorithms that do not rely on global knowledge. The algorithms presented here exploit similarities between subscriptions by using identity- and covering-tests, and by merging filters. While identity-based routing is a simplified version of covering-based routing, merging-based routing is more advanced because it exploits the concept of filter merging. Furthermore, the idea of imperfect routing algorithms is introduced. The thesis consists of a theoretical and a practical part. The theoretical part presents a formal specification of publish/subscribe systems, a routing framework and a set of routing algorithms, and discusses how the routing optimizations can be broken down to the actual data/filter model. The practical part presents the implementation of the Rebeca notification service which supports advertisements and all the routing algorithms mentioned above. A detailed practical evaluation of the implemented algorithms based upon the prototype is also presented