Robust execution of service workflows using redundancy and advance reservations

In this paper, we develop a novel algorithm that allows service consumers to execute business processes (or workflows) of interdependent services in a dependable manner within tight time-constraints. In particular, we consider large inter-organisational service-oriented systems, where services are offered by external organisations that demand financial remuneration and where their use has to be negotiated in advance using explicit service-level agreements (as is common in Grids and cloud computing). Here, different providers often offer the same type of service at varying levels of quality and price. Furthermore, some providers may be less trustworthy than others, possibly failing to meet their agreements. To control this unreliability and ensure end-to-end dependability while maximising the profit obtained from completing a business process, our algorithm automatically selects the most suitable providers. Moreover, unlike existing work, it reasons about the dependability properties of a workflow, and it controls these by using service redundancy for critical tasks and by planning for contingencies. Finally, our algorithm reserves services for only parts of its workflow at any time, in order to retain flexibility when failures occur. We show empirically that our algorithm consistently outperforms existing approaches, achieving up to a 35-fold increase in profit and successfully completing most workflows, even when the majority of providers fail

Equilibrium and Learning in Queues with Advance Reservations

Consider a multi-class preemptive-resume $M/D/1$ queueing system that supports advance reservations (AR). In this system, strategic customers must decide whether to reserve a server in advance (thereby gaining higher priority) or avoid AR. Reserving a server in advance bears a cost. In this paper, we conduct a game-theoretic analysis of this system, characterizing the equilibrium strategies. Specifically, we show that the game has two types of equilibria. In one type, none of the customers makes reservation. In the other type, only customers that realize early enough that they will need service make reservations. We show that the types and number of equilibria depend on the parameters of the queue and on the reservation cost. Specifically, we prove that the equilibrium is unique if the server utilization is below 1/2. Otherwise, there may be multiple equilibria depending on the reservation cost. Next, we assume that the reservation cost is a fee set by the provider. In that case, we show that the revenue maximizing fee leads to a unique equilibrium if the utilization is below 2/3, but multiple equilibria if the utilization exceeds 2/3. Finally, we study a dynamic version of the game, where users learn and adapt their strategies based on observations of past actions or strategies of other users. Depending on the type of learning (i.e., action learning vs.\ strategy learning), we show that the game converges to an equilibrium in some cases, while it cycles in other cases

Selective Advance Reservations Based on Host Movement Detection and Resource-Aware Handoff

This paper proposes a new mechanism, which addresses the excessive advance reservation requirements of QoS guarantee methods for mobile Internet. To save resources for excessive advance reservations, the proposed mechanism employs a movement detection scheme for a mobile host (MH) using link-layer functionalities. With the movement detection scheme, advance reservations can be established at only where a MH is likely to visit soon. Another novel feature of our mechanism is resource-aware handoff direction scheme that allows a MH to choose its next BS according to not only the link-layer signal strength, but also the available amount of resources in the reachable base stations (BSs). It considerably decreases a probability that QoS is disrupted due to the failure in advance reservation request. Also, the proposed mechanism requires fewer functional and structural changes to the current Internet components and protocols since all the enhanced features are integrated only into leaf BSs and MHs. It does not suffer from the problems of the conventional approaches based on Mobile IP and RSVP Tunnel, such as non-optimal routing path and signalling overhead. Our experiment results show that the proposed mechanism successfully eliminates the overhead for useless advance reservations while guaranteeing seamless QoS for MHs. The performance comparison demonstrates that our mechanism slightly outperforms the conventional approaches while requiring fewer modifications and additions to the existing Internet architecture. This performance advantage of the proposed mechanism becomes noticeable when the network is congested and the mobility of a host is high. Copyright © 2006 John Wiley & Sons, Ltd

Selective Advance Reservations Based on Host Movement Detection and Resource-Aware Handoff

This paper proposes a new mechanism, which addresses the excessive advance reservation requirements of QoS guarantee methods for mobile Internet. To save resources for excessive advance reservations, the proposed mechanism employs a movement detection scheme for a mobile host (MH) using link-layer functionalities. With the movement detection scheme, advance reservations can be established at only where a MH is likely to visit soon. Another novel feature of our mechanism is resource-aware handoff direction scheme that allows a MH to choose its next BS according to not only the link-layer signal strength, but also the available amount of resources in the reachable base stations (BSs). It considerably decreases a probability that QoS is disrupted due to the failure in advance reservation request. Also, the proposed mechanism requires fewer functional and structural changes to the current Internet components and protocols since all the enhanced features are integrated only into leaf BSs and MHs. It does not suffer from the problems of the conventional approaches based on Mobile IP and RSVP Tunnel, such as non-optimal routing path and signalling overhead. Our experiment results show that the proposed mechanism successfully eliminates the overhead for useless advance reservations while guaranteeing seamless QoS for MHs. The performance comparison demonstrates that our mechanism slightly outperforms the conventional approaches while requiring fewer modifications and additions to the existing Internet architecture. This performance advantage of the proposed mechanism becomes noticeable when the network is congested and the mobility of a host is high. Copyright © 2006 John Wiley & Sons, Ltd

Advance reservations and information sharing in queues with strategic customers

In many branches of the economy, including transportation, lodging, and more recently cloud computing, users can reserve resources in advance. Although advance reservations are gaining popularity, little is known about the strategic behavior of customers facing the decision whether to reserve a resource in advance or not. Making an advance reservation can reduce the waiting time or the probability of not getting service, but it is usually associated with an additional cost. To evaluate this trade-off, we develop a game-theoretic framework, called advance reservation games, that helps in reasoning about the strategic behavior of customers in systems that allow advance reservations. Using this framework, we analyze several advance reservation models, in the context of slotted loss queues and waiting queues. The analysis of the economic equilibria, from the provider perspective, yields several key insights, including: (i) If customers have no a-priori information about the availability of servers, then only customers granted service should be charged a reservation fee; (ii) Informing customers about the exact number of available servers is less profitable than only informing them that servers are available; (iii) In many cases, the reservation fee that leads to the equilibrium with maximum possible profit leads to other equilibria, including one resulting with no profit; (iv) If the game repeats many times and customers update their strategy after observing actions of other customers at previous stage, then the system converges to an equilibrium where no one makes an advance reservation, if such an equilibrium exists. Else, the system cycles and yields positive profit to the provider Finally, we study the impact of information sharing in M/M/1 queues with strategic customers. We analyze the intuitive policy of sharing the queue length with customers when it is small and hiding it when it is large. We prove that, from the provider perspective, such a policy is never optimal. That is, either always sharing the queue length or always hiding it maximizes the average number of customers joining the queue

Advance Reservations for Distributed Real-Time Workflows with Probabilistic Service Guarantees

This paper addresses the problem of optimum allocation of distributed real-time workflows with probabilistic service guarantees over a Grid of physical resources made available by a provider. The discussion focuses on how such a problem may be mathematically formalised, both in terms of constraints and objective function to be optimized, which also accounts for possible business rules for regulating the deployment of the workflows. The presented formal problem constitutes a probabilistic admission control test that may be run by a provider in order to decide whether or not it is worth to admit new workflows into the system, and to decide what the optimum allocation of the workflow to the available resources is. Various options are presented which may be plugged into the formal problem description, depending on the specific needs of individual workflows

Real-Time Divisible Load Scheduling with Advance Reservation

Providing QoS and performance guarantees to arbitrarily di-visible loads has become a significant problem for many cluster-based research computing facilities. While progress is being made in scheduling arbitrarily divisible loads, previous ap-proaches have no support for advance reservations. However, with the emergence of Grid applications that require simulta-neous access to multi-site resources, supporting advance reser-vations in a cluster has become increasingly important. In this paper we propose a new divisible load real-time scheduling al-gorithm that supports advance reservations in a cluster. Our approach not only enforces the real-time agreement but also ad-dresses the under-utilization concerns raised by advance reser-vations. The impact of advance reservations on system perfor-mance is systematically studied. Simulation results show that, with the proposed algorithm and appropriate advance reserva-tions, the system performance could be maintained at the same level as the no reservation case.

Advance Reservations of Bandwidth in Computer Networks

In dieser Arbeit wurden die unterschiedlichen Aspekte untersucht, die die Leistungsfähigkeit eines Systems zur Vorausreservierung in Computer-Netzwerken bestimmen. Basierend auf einer Architektur, welche den Basisdienst für Vorausreservierungen mittels Multiprotocol Label Switching (MPLS) zur Verfügung stellt, wurden innerhalb eines Netzwerkmanagementsystems unterschiedliche Dienste implementiert und simulativ auf ihre Auswirkungen auf die Leistungsfähigkeit des Netzwerks in Bezug auf Anzahl zugelassener Datenströme sowie transportierte Datenmenge untersucht. Diese Dienste erweitern in entscheidendem Maße auch die Breite des Dienstangebots in Netzwerken im Vergleich zu bisherigen Implementierungen. So ist es möglich bei Angabe einer festen Datenmenge vom Netzwerkmanagement geeignete Übertragungszeiten und raten bestimmen zu lassen. Diese Parameter werden dann, zum Beispiel in Form von Service Level Agreements (SLA), vom Netzwerkmanagement garantiert und sind insbesondere in Umgebungen wichtig, in denen die Übertragung sehr großer Datenmengen notwendig ist, beispielsweise in Grid-Computing- Systemen. Die erweiterten Dienste dienen jedoch nicht nur den Nutzern, sondern sind auch für Betreiber interessant, da sie es ermöglichen die Leistungsfähigkeit des Netzwerkes zu erhöhen. Dies ist insbesondere zusammen mit weiteren Verfahren möglich, die die zusätzlich zur Verfügung stehenden Informationen über zeitliche Aspekte, wie die Dauer von Übertragungen, nutzen. Im Vergleich zu den heute hauptsächlich betrachteten Systemen zur sog. unmittelbaren Reservierung, kann bei geschicktem Einsatz der hier implementierten Dienste und Verfahren eine deutliche Verbesserung der Leistung erzielt werden. Hinzu kommen bei Vorausreservierungen die erheblichen Vorteile für die Nutzer eines Netzwerkes, wie z.B. der oben beschriebene Datentransfer. Die Leistung eines Netzwerkes bemisst sich jedoch nicht nur an der transportierten Datenmenge, sondern auch am Verhalten im Fehlerfall und der Geschwindigkeit des Managementsystems. Dazu wurden im Rahmen dieser Arbeit mögliche Strategien zur Reaktion von Vorausreservierungssystemen im Fall von Link-Ausfällen entwickelt und untersucht. Auch hier kommt dem zeitlichen Aspekt eine wichtige Bedeutung zu. Es erwies sich als erfolgreich, nicht nur unmittelbar betroffene Datenströme sondern auch solche, die zwar bereits bekannt, jedoch noch nicht aktiv waren, in die Fehlerbehandlungsstrategie mit einzubeziehen. Datenstrukturen, die von der Zugangskontrolle des Managementsystems benötigt werden und dort die Geschwindigkeit maßgeblich bestimmen, wurden unter den Aspekten der Zugriffsgeschwindigkeit und des Speicherverbrauchs untersucht. Hierbei wurde gezeigt, dass Arrays erhebliche Vorteile im Hinblick auf beide Aspekte haben und in den meisten Fällen einer Baumstruktur, die speziell für die Aufgabe innerhalb der Zugangskontrolle entwickelt wurde, überlegen sind. Die Nutzung von Vorausreservierungen in Computer-Netzwerken ist damit eine nützliche und wichtige Erweiterung der Funktionalität eines Netzwerkes sowohl in Bezug auf das zur Verfügung stehende Angebot an Diensten, als auch im Hinblick auf die Leistungsfähigkeit des Netzwerkes.In this thesis, the impact of using advance reservations of bandwidth in a computer network on the performance for both clients and operators of the network is examined. Based on an architecture that uses multi-protocol label switching (MPLS) controlled by bandwidth brokers, a number of services that - compared to todays best-effort or immediate reservation networks - provide an enhanced functionality for clients were developed. These services allow clients to specify requests in a less stringent way than currently necessary, for example, it is possible to define only the amount of data to be transmitted between two network endpoints and the management system then determines suitable transmission parameters such as start and stop time and transmission rate. This functionality provides reliable feedback to clients and can serve as a foundation for providing service-level agreements, e.g., guaranteeing deadlines for the transmission of a certain amount of data. The additional services can also be used by network operators to improve the overall utilization of the network. In addition, the various opportunities of using the additional temporal dimension of the advance reservation service are suitable to improve the network performance. It can be shown that the amount of blocked requests and bandwidth can be considerably decreased making use of both services and the additional information available in the given environment. Besides the achievable throughout and amount of admitted requests, the term performance in the context of advance reservation systems also covers other aspects such as failure recovery strategies and the processing time required by the network management system. In the thesis, several strategies to be applied in case of link failures are outlined and examined with respect to their applicability and achievable performance. For example, it can be shown that it is worthwhile to consider not only flows which are active at the time a failure occurs but also to take inactive but already admitted flows into account in order to achieve the best possible performance. In addition to failure recovery, also the processing speed of the management system is of importance. For that purpose, in particular the data structures used to store the current and future network status need to be examined since they dominate the processing time of the management system. Two data structures, arrays and a tree which was especially designed for this purpose were examined, showing that arrays are superior with respect to processing speed and memory consumption in almost any environment

On the Impact of Advance Reservations for Energy-Aware Provisioning of Bare-Metal Cloud Resources

International audienceThis work investigates factors that can impact the elasticity of bare-metal resources. We analyse data from a real bare-metal deployment system to build a deployment time model, which is used to evaluate how provisioning time impacts the reservation of bare-metal resources. Climate/Blazar, a reservation framework designed for OpenStack, is discussed. Simulation results show that reservations can help reduce the time to deliver a provisioned cluster to its customer while achieving energy savings similar to those of strategies that switch-off idle resources