SLA guarantees for cloud services

Quality-of-service and SLA guarantees are among the major challenges of cloud-based services. In this paper we first present a new cloud model called SLAaaS — SLA aware Service. SLAaaS considers QoS levels and SLA as first class citizens of cloud-based services. This model is orthogonal to other SaaS, PaaS, and IaaS cloud models, and may apply to any of them. More specifically we make three contributions: (i) we provide a novel domain specific language that allows to describe QoS-oriented SLA associated with cloud services; (ii) we present a general control-theoretic approach for managing cloud service SLA; (iii) we apply the proposed language and control approach to guarantee SLA in various case studies, ranging from cloud-based MapReduce service, to locking service, and higher-level e-commerce service; these case studies successfully illustrate SLA management with different QoS aspects of cloud services such as performance, dependability, financial energetic costs.     

面向云联网的云服务协商机制

随着云计算的快速发展,越来越多的用户开始使用云服务提供商提供的服务,而云联网作为云计算研究的新领域,可以实现跨云服务提供商的服务,当单个云服务提供商无法满足用户的服务需求时,云服务提供商之间以合作的方式为用户提供服务,以便更好地满足用户的服务需求。针对上述情况,提出了面向云联网的云服务协商机制,该机制利用云联网和改进的经典合同网模型来实现云服务提供商的交互协商。为了有效地选出合作伙伴以提高合作效率,还为每一个云服务提供商建立了一个熟人集。实验表明,本文设计的机制可以有效地提高云服务提供商之间的合作效率,并且可以更好地满足用户的服务需求。     

Analysis of a trust model for SLA negotiation and enforcement in cloud markets

Online Reputation Systems help mitigate the information asymmetry between clients and providers in Cloud Computing Markets. However, those systems raise two main drawbacks: the disagreement for assuming the cost of ownership of such services and their vulnerability to reputation attacks from dishonest parties that want to increase their reputation. This article faces both problems by describing a decentralised (peer-to-peer) trust model that does not require the intervention of a central entity to manage it. This model includes mechanisms to allow participants to avoid dishonest behaviour from other peers: each client statistically analyses the external reports about providers and updates the trustworthiness of the peers. The trustworthiness values will be used to negotiate prices in later transactions. The trust model is then incorporated in the Service-Level Agreement negotiation and enforcement processes, prioritising trusted clients over non-trusted clients to minimise the consequences of low Quality of Service in relation to the trust of the provider, and incentivise accurate trust reports from the clients. Finally, this article evaluates and discusses the validity of the trust model under different attacks from dishonest clients and providers.     

云计算中基于SLA的服务可信协商与访问控制策略

针对当前云计算中因服务提供者(SP)的信任保障机制缺失而容易被不可信服务消费者(SC)滥用的现象,提出面向SC实体的服务可信协商及访问控制策略.该策略首先依据系统信任规则来表达服务实体的可信程度,然后通过求解SC实体的直接和间接信任推理空间建立信任证据的举证方法,同时采用服务级别协议(service level agreements,SLA)构建交互双方的协商机制,最后综合信任传递与迭代计算策略,确定服务交互的SLA等级,提供相应级别的服务,从而达到访问控制的目的.理论分析与实验结果表明,该方法虽少量增加了协商的次数,但能较好解决服务被滥用以及利用率不高的问题,为云计算环境下信任协商研究提供一种有效的新方法.     

SLA negotiation and enforcement policies for revenue maximization and client classification in cloud providers

In Cloud Computing markets, owners of computing resources negotiate with their potential clients to sell computing power. The terms of the Quality of Service (QoS) to be provided as well as the economic conditions are established in a Service-Level Agreement (SLA). The common objective of a Cloud provider is to maximize its economic profit. However, there are situations in which providers must differentiate the SLAs with respect to the type of client that is willing to access the resources or the agreed QoS, e.g. when the hardware resources are shared between users of the company that own the resources and external users.This article proposes two sets of policies to manage SLAs with respect to the business objectives of a Cloud provider: Revenue Maximization or classification of clients. The criterion to classify clients is established according to the relationship between client and provider (external user, internal or another privileged relationship) and the QoS that the client purchases (cheap contracts or extra QoS by paying an extra fee). The validity of the policies is demonstrated through exhaustive experiments.     

An optimization approach for cloud composite services

Recently, a considerable literature has grown up around the theme of composite services verification. Namely, the verification of the non-functional aspect generally consisting of optimizing the quality of service (QoS) of the composite service. Great efforts have been devoted to the study of several optimization methods and their impact on the QoS of the composite service. Guaranteeing the service level agreements established with users remains one of the greatest challenges in this field. This essay explores a new composition approach based on a linear programming algorithm and compares the obtained results with existing works. Our approach aims to guarantee an efficient and optimal solution to the Cloud composite service problem. For evaluation, we have developed the CR-SIM simulator that selects and composes services in the Cloud context.

     

A three-phase energy-saving strategy for cloud storage systems

In the running process of cloud data center, the idle data nodes will generate a large amount of unnecessary energy consumption. Furthermore, the resource misallocation will also cause a great waste of energy. This paper proposes a three-phase energy-saving strategy named TPES in order to save energy and operational costs for cloud suppliers. The three phases are replica management based on variable replication factor, cluster reconfiguration according to the optimal total costs and state transition based on observed and predicted workloads. These three phases save energy for the system at different levels which enhance the adaptability of our strategy. We evaluate our strategy using the expanded CloudSim toolkit and the results show that the proposed strategy achieves better energy reduction under different conditions in comparison with the existing schemes.     

A trust negotiation system for digital library Web services

A scalable approach to trust negotiation is required in digital library (DL) environments that have large and dynamic user populations. In this paper we introduce Trust-Serv, a model-driven trust negotiation framework for Web services, and show how it can be used to effectively handle trust negotiation in DLs. The framework employs a model for trust negotiation based on state machines, extended with security abstractions. High-level specifications expressed with the state-machine-based model are then translated into formats suitable for automating the trust negotiation process. The proposed framework also supports negotiation policy lifecycle management, an important trait in the dynamic environments that characterize DLs. In particular, we present a set of policy change operations that enable the dynamic evolution of negotiation policies without disrupting ongoing negotiations. The proposed approach has been implemented as a container-centric mechanism that is transparent to the DL and to the developers of DL Web services, simplifying DL development and management as well as enabling scalable deployments.     

A P2P strategy for QoS discovery and SLA negotiation in Grid environment

In recent years, Grid systems and Peer to Peer networks are the most commonly-used solutions to achieve the same goal: the sharing of resources and services in heterogeneous, dynamic, distributed environments. Many studies have proposed hybrid approaches that try to conjugate the advantages of the two models. This paper proposes an architecture that integrates the P2P interaction model in Grid environments, so as to build an open cooperative model wherein Grid entities are composed in a decentralized way. In particular, this paper focuses on a QoS aware discovery algorithm for P2P Grid systems, analyzing protocol and explaining techniques used to improve its performance.     

A similarity measure for the negotiation in web services

This paper presents a new negotiation approach integrating a similarity-based metric to measure the client’s satisfaction level by quantifying the correspondence between the features required by the client and the ones proposed by the service. This negotiation process is integrated within an adaptation platform for multimedia presentations supporting different types of terminals. The negotiation and adaptation processes are based on the management of user’s and service’s profiles. We also propose an extension of the SIP protocol to ensure the communication between the client and the server by defining new functionalities.     

Extending OCCI for an autonomous SLA negotiation strategy in federated clouds

Each cloud service provider provides only an interface of its own cloud infrastructure for enabling clients to use its cloud resources. However, there is a number of difficulties for cloud providers to ensure proper functioning. One of the main problems of a cloud provider is the lack of resources to support a huge number of on-demand resources provisioning. Thus, resources cannot be distributed among different cloud providers since the federation is not the basic operation of the cloud provider. The most efficient way to overcome this problem is to extend the interface's cloud provider with an automatic negotiation to dynamically form the best agreement between the different cloud providers based on the service level agreement. In this article, we propose an extension for the Open Cloud Computing Interface which is the standardized interface for the cloud computing to support the automatic negotiation between the different cloud providers. To prove the efficiency and the effectiveness of our approach, we implement a prototype to evaluate the key presented in this article.     

Model-driven trust negotiation for Web services

Trust negotiation is an approach to access control whereby access is granted based on trust established in a negotiation between the service requester and the service provider. Trust negotiation systems avoid several problems facing traditional access control models such as DAC (discretionary access control) and MAC (mandatory access control). Another problem is that Web service providers often do not know requesters identities in advance because of the ubiquitousness of services. We describe Trust-Serv, a trust negotiation framework for Web services, which features a policy language based on state machines. It is supported by lifecycle management and automated runtime enforcement tools. Credential retrieval and validation in Trust-Serv rely on predefined Web services that provide interactions with attribute assertion authorities and public key infrastructure.     

A novel approach to manage cloud security SLA incidents

Cloud computing is increasingly playing an important role in the service provisioning domain given the economic and technological benefits it offers. The popularity of cloud services is increasing but so are their customers’ concerns about security assurance and transparency of the Cloud Service Providers (CSPs). This is especially relevant in the case of critical services that are progressively moving to the cloud. Examples include the integrated European air traffic control system or public administrations through the governmental clouds. Recent efforts aim to specify security in cloud by using security service level agreements (secSLAs). However, the paucity of approaches to actually control the fulfillment of secSLAs and to react in case of security breaches, often results in distrust in cloud services. In this paper, we present a solution to monitor and enforce the fulfillment of secSLAs. Our framework is able to (a) detect occurrences that lead to unfulfillment of commitments, and (b) also provide mitigation to the harmful events that may or do compromise the validity of secSLAs.     

Chargeback for cloud services

With pay-per-use pricing models, elastic scaling of resources, and the use of shared virtualized infrastructures, cloud computing offers more efficient use of capital and agility. To leverage the advantages of cloud computing, organizations have to introduce cloud-specific chargeback practices. Organizations have to allocate IT service costs to business users in a way that reflects service consumption. To help organizations become effective users of cloud services, this article provides an overview of the factors that influence chargeback in the cloud services. This is an initial work that determines the factors influencing the chargeback in the cloud services. The findings of this research facilitate organizations to realize the implications of the cloud for their chargeback.     

A negotiation based scheduling for items with flexible process plans

A job-shop scheduling method is described utilizing a negotiation-based algorithm in autonomous distributed systems. Elements of a production system such as jobs and machines are regard as agents that act like an independent profit maker. A negotiation procedure is suggested including price-based bid construction and price revising mechanism. We propose a simulation-based iteration procedure in order to revise the decision making parameters. It is shown that the iterative procedure eventually improves the global performance of the entire system. The proposed method is expected to have flexibility against various system alternations, addition or deletion of jobs or sudden failure of machines. We develop a prototype software that utilizes the object oriented concept.     

云环境下自动信任协商机制研究

针对云计算环境带来的安全性问题,在目前云安全模型研究的基础上,对分层的云服务框架模型进行了安全性分析.综合考虑云计算环境特点,在不影响云服务质量的前提下保证数据安全,建立了一个云安全访问控制模型ACCP.该模型利用自动信任协商机制可以不依靠数据中心第三方安全服务,通过双方信任证集的交互和策略的控制自适应地建立组合安全域.通过在用户-服务以及组合服务之间两个场景下信任协商建立过程,表明了模型可行性和有效性.     

Generating recommendations for consensus negotiation in group personalization services

There are increasingly many personalization services in ubiquitous computing environments that involve a group of users rather than individuals. Ubiquitous commerce is one example of these environments. Ubiquitous commerce research is highly related to recommender systems that have the ability to provide even the most tentative shoppers with compelling and timely item suggestions. When the recommendations are made for a group of users, new challenges and issues arise to provide compelling item suggestions. One of the challenges a group recommender system must cope with is the potentially conflicting preferences of multiple users when selecting items for recommendation. In this paper, we focus on how individual user models can be aggregated to reach a consensus on recommendations. We describe and evaluate nine different consensus strategies and analyze them to highlight the benefits of group recommendation using live-user preference data. Moreover, we show that the performance is significantly different among strategies.     

Memory allocation algorithm for cloud services

Memory allocation has a major influence on multiuser systems, cloud-based services, virtual machines, and other computer systems. Memory allocation is a process that assigns physical or virtual memory space to programs and services as efficiently and quickly as possible. Economical memory allocation management needs allocation strategies with minimum wastage. In this paper, we introduce a new memory allocation algorithm based on sequential fits and zoning for on-demand (online) cloud services. The memory is divided into multiple zones, where a subgroup of relative request sizes compete in reverse order. We use simulation to compare our new mechanism with existing memory allocation methods that have been deployed using Amazon Elastic Compute Cloud as a test bed. The proposed algorithm is more efficient, and the average saving for the normalized revenue loss is about 7% better than best-fit and 15% better than first-fit memory allocation. In addition, we show that proposed algorithm is robust and faster and has a fairness index that is superior to that of existing techniques.     

A protocol for multi-agent negotiation in a group-choice decision making process

Negotiation is one of the most important features of agent interactions found in multi-agent systems, because it provides the basis for managing the expectations of the individual negotiating agents, and it enables selecting solutions that satisfy all the agents as much as possible. In order for negotiation to take place between two or more agents there is need for a negotiation protocol that defines the rules of the game; consequently, a variety of agent negotiation protocols have been proposed in literature. However, most of them are inappropriate for Group-Choice Decision Making (GCDM) because they do not explicitly exploit tradeoff to achieve social optimality, and their main focus is solving two-agent negotiation problems such as buyer–seller negotiation. In this paper we present an agent negotiation protocol that facilitates the solving of GCDM problems. The protocol is based on a hybrid of analytic and artificial intelligence techniques. The analytic component of the protocol utilizes a Game Theory model of an n-person general-sum game with complete information to determine the agreement options, while the knowledge-based (artificial intelligence) component of the protocol is similar to the strategic negotiation protocol. Moreover, this paper presents a tradeoff algorithm based on Qualitative Reasoning, which the agents employ to determine the ‘amount’ of tradeoff associated with various agreement options. Finally, the paper presents simulation results that illustrate the operational effectiveness of our agent negotiation protocol.