Efficient online monitoring of web-service SLAs

If an organization depends on the service quality provided by another organization it often enters into a bilateral service level agreement (SLA), which mitigates outsourcing risks by associating penalty payments with poor service quality. Once these agreements are entered into, it becomes necessary to monitor their conditions, which will commonly relate to timeliness, reliability and request throughput, at runtime. We show how these conditions can be translated into timed automata. Acceptance of a timed word by a timed automaton can be decided in quadratic time and because the timed automata can operate while messages are exchanged at runtime there is effectively only a linear run-time overhead. We present an implementation to derive on-line monitors for web services automatically from SLAs using an Eclipse plugin. We evaluate the efficiency and scalability of this approach using a large-scale case study in a service-oriented computational grid

Contract agreements via logic

We relate two contract models: one based on event structures and game theory, and the other one based on logic. In particular, we show that the notions of agreement and winning strategies in the game-theoretic model are related to that of provability in the logical model.Comment: In Proceedings ICE 2013, arXiv:1310.401

Efficient Online Timed Pattern Matching by Automata-Based Skipping

The timed pattern matching problem is an actively studied topic because of its relevance in monitoring of real-time systems. There one is given a log $w$ and a specification $\mathcal{A}$ (given by a timed word and a timed automaton in this paper), and one wishes to return the set of intervals for which the log $w$, when restricted to the interval, satisfies the specification $\mathcal{A}$. In our previous work we presented an efficient timed pattern matching algorithm: it adopts a skipping mechanism inspired by the classic Boyer--Moore (BM) string matching algorithm. In this work we tackle the problem of online timed pattern matching, towards embedded applications where it is vital to process a vast amount of incoming data in a timely manner. Specifically, we start with the Franek-Jennings-Smyth (FJS) string matching algorithm---a recent variant of the BM algorithm---and extend it to timed pattern matching. Our experiments indicate the efficiency of our FJS-type algorithm in online and offline timed pattern matching

A survey on online monitoring approaches of computer-based systems

This report surveys forms of online data collection that are in current use (as well as being the subject of research to adapt them to changing technology and demands), and can be used as inputs to assessment of dependability and resilience, although they are not primarily meant for this use

AUTONOMIC MANAGEMENT OF SOFTWARE AS A SERVICE SYSTEMS WITH MULTIPLE QUALITY OF SERVICE CLASSES

In recent years the emergence of Software as a Service (SaaS) provision and cloud computing in general had a tremendous impact on corporate information technology. While the implementation and successful operation of powerful information systems continues to be a cornerstone of success in modern enterprises, the ability to acquire IT infrastructure, software, or platforms on a pay-as-you-go basis has opened a new avenue for optimizing operational costs and processes. In this context we target elastic SaaS systems with on-demand cloud resource provisioning and implement an autonomic management artifact. Our framework forecasts future user behavior based on historic data, analyzes the impact of different workload levels on system performance based on a non-linear performance model, analyzes the economic impact of different provisioning strategies, derives an optimal operation strategy, and automatically assigns requests from users belonging to different Quality of Service (QoS) classes to the appropriate server instances. More generally, our artifact optimizes IT system operation based on a holistic evaluation of key aspects of service operation (e.g., system usage patterns, system performance, Service Level Agreements). The evaluation of our prototype, based on a real production system workload trace, indicates a cost-of-operation reduction by up to 60 percent without compromising QoS requirements

Service level agreements and virtual machines

Virtual machines (VMs) have been used for some time now, but only now with the newer and faster hardware that is being developed, now it is possible to consolidate many machines down to a single one running multiple instances of operating systems each with their own purpose. For as long as there have been users to use the servers, there has been the need for service level agreements. Now with the virtualization of services comes the need for a new breed of service level agreements. Service level agreements (SLAs) rarely exist for virtual servers unlike physical servers. Since this is the case, an effective SLA needs to be developed so the users of the virtual machines can know and be guaranteed their service like they were with the physical server. Questions such as, is it possible to take an existing service level agreement with the metrics from a physical server and transfer it directly to the virtual server? Are there changes that need to be made to the SLA in order for the SLA to be functional? These questions will be addressed in this study, along with a discussion on why changes would need to be made when moving a SLA to a virtual environment from a physical server. It is indeed possible to take most of the preexisting service level agreement that was written for a physical server and with modifications to metrics of CPU usage and memory utilization use it in a virtual environment. Additional metrics need to be made to the SLA when it is transferred to the virtual environment in order for the SLA to work effectively. These new metrics were found, tested and shown to be necessary in a virtual environment

Identifying Test Requirements by Analyzing SLA Guarantee Terms

Service Level Agreements (SLAs) are used to specify the negotiated conditions between the provider and the consumer of services. In this paper we present a stepwise method to identify and categorize a set of test requirements that represent the potential situations that can be exercised regarding the specification of each isolated guarantee term of an SLA. This identification is addressed by means of devising a set of coverage levels that allow grading the thoroughness of the tests. The utilization of these test requirements would focus on twofold objectives: (1) the generation of a test suite that allows exercising the situations described in the test requirements and (2) the support for the derivation of a monitoring plan that checks the compliance of these requirements at runtime. The approach is illustrated over an eHealth case study

Formal Verification of Service Level Agreements Through Distributed Monitoring

In this paper, we introduce a formal model of the availability, budget compliance and sustainability of istributed services, where service sustainability is a new concept which arises as the composition of service availability and budget compliance. The model formalizes a distributed platform for monitoring the above service characteristics in terms of a parallel composition of task automata, where dynamically generated tasks model asynchronous events with deadlines. The main result of this paper is a formal model to optimize and reason about service characteristics through monitoring. In particular, we use schedulability analysis of the underlying timed automata to optimize and guarantee service sustainability

ASSOCIATING USER’S PSYCHOLOGY INTO QUALITY OF SERVICE: AN EXAMPLE OF WEB ADAPTATION SERVICES

Content adaptation is a potential solution for tailoring multimedia web content according to the users’ preferences and heterogeneous devices’ constraints. Content adaptation can be done as third party service over the Internet. Users may pay for the service thus demand quality. The quality should include the human psychological factors. One of these factors is the maximum time a user can wait for the output to be displayed. Thus, response time is one of the qualities of service (QoS) to be considered in assessing the deliverability of content adaptation services. However, the advertised response time may not be deliverable accordingly during the actual service execution due to heavy load. Practically, the service provider should able to determine a current deliverable response time before the service level agreement (SLA) is settled with the users. In this paper, we propose a strategy for service providers to evaluate incoming requests and capable of offering the new response time. The proposed strategy takes into account the current server load and enables a mechanism for the user to evaluate whether the new response time can be accepted or not. We analyzed the performance of the proposed strategy in terms of SLA settlement under various conditions. The results indicate that the proposed strategy performs well

Web Services Metrics: A Survey and A Classification

Abstract. Web Services have emerged as a new Web-based technology paradigm for exchanging information on the Internet using platform-neutral standards, such as XML and adopting Internet-based protocols. They have become a promising technology to design and build complex inter-enterprise business applications. However, Web Services are problematic to measure, control, and manage. Software metrics is vital for the management, control, and measurement of software development and despite the vast amount of techniques/mechanisms and metrics for traditional and Object-Oriented software, there has been a few research and techniques that deals with metrics for Web Services. As companies increasingly invest and relies on Web Services, the importance of metrics for those services continues to grow. In this paper I present and classify the existing metrics for Web Services, and discuss their usage and benefits. In addition, I highlight the problems found in using some of the metrics and discuss what is still lacking in this domain