Runtime monitoring of service based systems

With the growing popularity of web services the demand of highly reliable service based systems (SBS) is increasing. Formal verification and testing are performed to ensure the correctness of a system before it is deployed in a real environment. But the high complexity of complete fielded systems puts their effectiveness into questions. Runtime monitoring is the potential technique to cover the area not covered by formal verification and testing. This technique aims to assure the correctness of the current execution of a system. Substantial amount of research has been carried out in runtime monitoring to ensure the reliability of autonomous legacy software. However in service based system some significant complications arises as they focus on systems with no autonomous components, that make the approaches applied to monitor legacy software inadequate for service based system. In this thesis we present a framework for runtime monitoring of service based systems. We establish the necessity of introducing new types of inconsistencies beyond the classical inconsistencies that may occur during the execution of service based systems and develop reasoning mechanism to detect them at run time. In the proposed framework, the properties to be monitored include: (i) behavioural properties of the co-ordination process of the service based system, (ii) functional properties that express functional requirements for the individual services of a service based system or groups of such services, (ii) assumptions regarding the behaviour of the service based system and its constituent services and their effects on the state of the system and (iii) Quality-of- Service (QOS) properties for the service based systems and its constituent services. All types of properties are expressed in a property specification language which is based on event- calculus [Sha99]. The behavioural properties to be monitored at run-time are extracted automatically from the specification of the co-ordination process of a service-based system in BPEL [Bpe03] while the other types of properties to be monitored must be specified by the providers of the system. These properties must be specified in terms of: (i) events that can be observed at run-time and correspond to either operation invocation and response messages or the assignment of values to global variables used by the co-ordination process of the system, and (ii) conditions over the state of the co-ordination process of the system and/or the individual services deployed by it. These restrictions ensure that property monitoring can be based solely on events which are generated by virtue of the normal operation of the system without the need for instrumenting the individual services deployed by it. The property specification language that is used by this framework is a first-order logic language that incorporates special predicates to signify assertions about time and, to this end, it provides a very expressive framework for specifying properties of service based system, which may include temporal characteristics. At run-time, the framework deploys an event receiver that catches events which are exchanged by the different services and the co-ordination process of the system and stores them in an event database. This database is accessed by a monitor that can detect different types of violations of properties. These types are: (i) violations of functional properties and quality-of-service properties by the recorded behaviour of the service based system, (ii) violations and potential violations of behavioural properties, functional properties and quality- of-service properties by the expected system behaviour, and (iii) unjustified and potentially unjustified actions which the system has taken by wrongly assuming that certain pre-conditions associated with the undertaken actions were satisfied at run-time. The detection of these types of violations is fully automatic and is based on an algorithm that has been developed as a variant of algorithms for integrity constraint checking in temporal deductive databases [Ple93, Cho95]. We have implemented a prototype of the proposed monitoring framework and showed the effectiveness of the monitoring prototype through several case studies

A Framework for Hierarchical and Recursive Monitoring of Service Based Systems

Runtime monitoring of Service Based Systems (SBSs) usually relies on information derived from I/O messages exchanged within business processes implementing services. When service provisioning is regulated by complex Service Level Agreements (SLAs) between service requesters, (composed) services, and infrastructure providers, monitoring may require additional features, such as (i) coordination among events captured at different sources involved in service provisioning and (ii) delegation of properties monitoring to local sites. This paper discusses an architecture and engagement protocol supporting the two aforementioned requirements for monitoring complex SLA-driven service provisioning

Advanced service monitoring configurations with SLA decomposition and selection

Service Level Agreements (SLAs) for Software Services aim to clearly identify the service level commitments established between service requesters and providers. The commitments that are agreed however can be expressed in complex notations through a combination of expressions that need to evaluated and monitored efficiently. The dynamic allocation of the responsibility for monitoring SLAs (and often different parts within them) to different monitoring components is necessary as both SLAs and the components available for monitoring them may change dynamically during the operation of a service based system. In this paper we discuss an approach to supporting this dynamic configuration, and in particular, how SLAs expressed in higher-level notations can be efficiently decomposed and appropriate monitoring components dynamically allocated for each part of the agreements. The approach is illustrated with mechanical support in the form of a configuration service which can be incorporated into SLA-based service monitoring infrastructures

Dynamic set-up of monitoring infrastructures for service based systems

Service based systems are intrinsically dynamic as the services deployed by them can be replaced at runtime. When this happens, the Service Level Agreements (SLAs) that regulate the provision of services may also need to change. Following such changes, the monitoring infrastructure that is used to monitor SLAs may also need to be modified to ensure the continuous provision of the necessary runtime checks. This paper presents a framework that supports the dynamic assessment of the monitorability of SLAs terms and the dynamic setup of an appropriate infrastructure for monitoring them following such changes. The monitorability checks are based on comparisons between the SLA terms for specific services and descriptions of the monitoring capabilities of these services which are expressed in languages introduced in the paper. The paper presents a prototype implementation of the framework and the results of a preliminary evaluation of it

A monitoring approach for runtime service discovery

Effective runtime service discovery requires identification of services based on different service characteristics such as structural, behavioural, quality, and contextual characteristics. However, current service registries guarantee services described in terms of structural and sometimes quality characteristics and, therefore, it is not always possible to assume that services in them will have all the characteristics required for effective service discovery. In this paper, we describe a monitor-based runtime service discovery framework called MoRSeD. The framework supports service discovery in both push and pull modes of query execution. The push mode of query execution is performed in parallel to the execution of a service-based system, in a proactive way. Both types of queries are specified in a query language called SerDiQueL that allows the representation of structural, behavioral, quality, and contextual conditions of services to be identified. The framework uses a monitor component to verify if behavioral and contextual conditions in the queries can be satisfied by services, based on translations of these conditions into properties represented in event calculus, and verification of the satisfiability of these properties against services. The monitor is also used to support identification that services participating in a service-based system are unavailable, and identification of changes in the behavioral and contextual characteristics of the services. A prototype implementation of the framework has been developed. The framework has been evaluated in terms of comparison of its performance when using and when not using the monitor component

Context Aware Web-Service Monitoring

Monitoring the correct behaviour of a service-based system is a necessity and a key challenge in Service Oriented Computing. Several efforts have been directed towards the development of approaches dealing with the monitoring activity of service-based systems. However, these approaches are in general not suitable when dealing with modifications in service-based systems. Furthermore, existing monitoring approaches do not take into consideration the context of the users and how this context may affect the monitor activity. Consequently, a holistic monitor approach, capable of dealing with the dynamic nature of service-based systems and of taking into consideration the user context, would be highly desirable. In this thesis we present a monitor adaptation framework capable of dealing with changes in a service-based system and different types of users interacting with it. More specifically, the framework obtains a set of monitor rules, necessary to verify the correct behaviour of a service-based system, for a particular user. Moreover, the monitor rules verifying the behaviour of a service-based system relate to properties of the context types defined for a user. The main contributions of our work include the general characterisation of a user interacting with a service-based system and the generation of suitable monitor rules.The proposed framework can be applied to any service composition without the need of further modifications. Our work complements previous research carried on in the area of web service monitoring. More specifically, our work generates a set of suitable monitor rules - related to the user context - which are deployed in a run-time monitor component. Our framework has been tested and validated in several cases considering different scenarios

Runtime monitoring of service based systems

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A framework for hierarchical and recursive monitoring of service based systems

Runtime monitoring of Service Based Systems (SBSs) usually relies on information derived from I/O messages exchanged within business processes implementing services. When service provisioning is regulated by complex Service Level Agreements (SLAs) between service requesters, (composed) services, and infrastructure providers, monitoring may require additional features, such as (i) coordination among events captured at different sources involved in service provisioning and (ii) delegation of properties monitoring to local sites. This paper discusses an architecture and engagement protocol supporting the two aforementioned requirements for monitoring complex SLA-driven service provisioning