Service-Level Agreements for Service-Oriented Computing

Abstract. Service-oriented computing is dynamic. There may be many possible service instances available for binding, leading to uncertainty about where service requests will execute. We present a novel Markovian process calculus which allows the formal expression of uncertainty about binding as found in service-oriented computing. We show how to compute meaningful quantitative information about the quality of service provided in such a setting. These numerical results can be used to allow the expression of accurate service-level agreements about service-oriented computing.

Monitoring Dependencies for SLAs: The MoDe4SLA Approach

In service oriented computing different techniques for monitoring Service Level Agreements (SLAs) are available. Many of these monitoring approaches focus on bilateral agreements between partners. However, when monitoring composite services it is not only important to figure out whether SLAs are violated, but we also need to analyze why these violations have occurred. When offering a composite service a company depends on its content providers to meet the service level they agreed upon. Due to these dependencies a company should not only monitor the SLA of the composite service, but also the SLAs of the services it depends on. By analyzing and monitoring the composite service in this way, causes for SLA violations can be easier found. In this paper we demonstrate how to analyze SLAs during development phase and how to monitor these dependencies using event logs during runtime. We call our approach MoDe4SLA (Monitoring Dependencies for SLAs)

An interoperable and self-adaptive approach for SLA-based service virtualization in heterogeneous Cloud environments

Cloud computing is a newly emerged computing infrastructure that builds on the latest achievements of diverse research areas, such as Grid computing, Service-oriented computing, business process management and virtualization. An important characteristic of Cloud-based services is the provision of non-functional guarantees in the form of Service Level Agreements (SLAs), such as guarantees on execution time or price. However, due to system malfunctions, changing workload conditions, hard- and software failures, established SLAs can be violated. In order to avoid costly SLA violations, flexible and adaptive SLA attainment strategies are needed. In this paper we present a self-manageable architecture for SLA-based service virtualization that provides a way to ease interoperable service executions in a diverse, heterogeneous, distributed and virtualized world of services. We demonstrate in this paper that the combination of negotiation, brokering and deployment using SLA-aware extensions and autonomic computing principles are required for achieving reliable and efficient service operation in distributed environments. © 2012 Elsevier B.V. All rights reserved

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

A reference architecture for multi-level SLA management

There is a global trend towards service-orientation, both for organizing business interactions but also in modern IT architectures. At the business-level, service industries are becoming the dominating sector in which solutions are flexibly composed out of networked services. At the IT level, the paradigms of Service-Oriented Architecture and Cloud Computing realize service-orientation for both software and infrastructure services. Again, flexible composition across different layers is a major advantage of this paradigm. Service Level Agreements (SLA) are a common approach for specifying the exact conditions under which services are to be delivered and, thus, are a prerequisite for supporting the flexible trading of services. However, typical SLAs are just specified at a single layer and do not allow service providers to manage their service stack accordingly. They have no insight on how SLAs at one layer translate to metrics or parameters at the various lower layers of the service stack. In this paper, we present a reference architecture for a multi-level SLA management framework. We discuss the fundamental concepts and detail the main architectural components and interfaces. Furthermore, we show how the framework can be flexibly used for different industrial scenarios

A WS-Agreement Based SLA Implementation for the CMAC Platform

The emerging transformation from a product oriented economy to a service oriented economy based on Cloud environments envisions new scenarios where actual QoS (Quality of Service) mechanisms need to be redesigned. In such scenarios new models to negotiate and manage Service Level Agreements (SLAs) are necessary. An SLA is a formal contract which defines acceptable service levels to be provided by the Service Provider to its customers in measurable terms. SLAs are an essential component in building Cloud systems where commitments and assurances are specified, implemented, monitored and possibly negotiable. This is meant to guarantee that consumers’ service quality expectations can be achieved. In fact, the level of customer satisfaction is crucial in Cloud environments, making SLAs one of the most important and active research topics. This paper presents an SLA implementation for negotiation, monitoring and renegotiation of agreements for Cloud services based on the CMAC (Condition Monitoring on A Cloud) platform. CMAC offers condition monitoring services in cloud computing environments to detect events on assets as well as data storage services

Towards Deployments Contracts in Large Scale Clusters & Desktop Grids

While many dream and talk about Service Level Agreement (SLA) and Quality of Service (QoS) for Service Oriented Architectures (SOA), the practical reality of Grid computing is still far from providing effective techniques enabling such contractual agreements. Towards this goal, this paper provides an overview of the techniques offered by ProActive to set and use contractual agreements. Based on the identification of roles, application developer, infrastructure manager, application user, the actors of a Grid environment can specify what is required or what is provided at various levels. The results are both flexibility and adaptability, matching the application constraints and the environment characteristics with various techniques

Automatic Parameter Optimisation of Service Quality and Resource Usage

Developers use models to design real world distributed applications that often are subject to Service Level Agreements to find a good balance between the quality of the service and its resource usage. Executable models has been used to observe and study such applications using, e.g., the Real Time ABS language, an executable and object-oriented modelling language.For complex models, due to the high number and dependencies between the parameters, it is very difficult to understand the best possible setting that leads the system towards a desired quality of service, while minimising the usage of computing resources. In this work we present POPT, a parameter optimiser tool that starting from Real Time ABS models, by using AI techniques, searches in an automatic way for the best possible setting to satisfy the developer’s expectations

Modelling service-oriented computing with temporal symbolic graph transformation systems

In this paper, we present a novel semantics for an essential aspect of service-oriented computing: the mechanism through which systems evolve through a symbiosis of state transformations and run-time service discovery and binding. The semantics is based on a new notion of temporal symbolic graph-transformation systems: in temporal symbolic graphs, interfaces can be specified using temporal logic, and service-level agreements can be specified in that logic's propositional fragment. An important advantage of our framework is that it can be supported by tools that implement temporal symbolic graph transformations, which would also provide a means of animating service-oriented systems evolution. We illustrate our semantics with a simple trip-booking service.Preprin

A decentralized service discovery approach on peer-to-peer network

Service-Oriented Computing (SOC) is emerging as a paradigm for developing distributed applications. A critical issue of utilizing SOC is to have a scalable, reliable, and robust service discovery mechanism. However, traditional service discovery methods using centralized registries can easily suffer from problems such as performance bottleneck and vulnerability to failures in large scalable service networks, thus functioning abnormally. To address these problems, this paper proposes a peer-to-peer-based decentralized service discovery approach named Chord4S. Chord4S utilizes the data distribution and lookup capabilities of the popular Chord to distribute and discover services in a decentralized manner. Data availability is further improved by distributing published descriptions of functionally equivalent services to different successor nodes that are organized into virtual segments in the Chord4S circle. Based on the service publication approach, Chord4S supports QoS-aware service discovery. Chord4S also supports service discovery with wildcard(s). In addition, the Chord routing protocol is extended to support efficient discovery of multiple services with a single query. This enables late negotiation of Service Level Agreements (SLAs) between service consumers and multiple candidate service providers. The experimental evaluation shows that Chord4S achieves higher data availability and provides efficient query with reasonable overhead