Dependability analysis of web services

Web Services form the basis of the web based eCommerce eScience applications so it is vital that robust services are developed. Traditional validation and verification techniques are centred around the concept of removing all faults to guarantee correct operation whereas Dependability gives an assessment of how dependably a system can deliver the required functionality by assessing attributes, and by eliminating threats via means attempts to improve dependability. Fault injection is a well-proven dependability assessment method. Although much work has been done in the area of fault injection and distributed systems in general, there appears to have been little research carried out on applying this to middleware systems and Web Services in particular. There are additional problems associated with applying existing fault injection technologies to Web Services running in a virtual machine environment since most are either invasive or work at a machine level. The Fault Injection Technology (FIT) method has been devised to address these problems for middleware systems. The Web Service-Fault Injection Technology (WS-FIT) implementation applies the FIT method, based on network level fault injection, to Web Services to create a non-invasive dependability assessment method. It allows targeted perturbation of Web Service RFC parameters as well as more traditional network level fault injection operations. The WS-FIT tool includes taxonomies that define a system under test, fault models to apply and failure modes to be detected, and uses these taxonomies to generate fault injection campaigns. WS-FIT has been applied to a number of case studies and has successfully demonstrated its effectiveness. It has also been successfully applied to a third-party system to evaluate dependability means. It performed this dependability assessment as well as allowing debugging of the means to be undertaken uncovering unknown faults

Dependability Assessment of an OGSA Compliant Middleware Implementation by Fault Injection

This paper presents our research on applying our dependability assessment method to an OGSA compliant middleware product. Our initial proof of concept experiment was implemented using a stateless Tomcat web server and Apache SOAP. This research adapts and enhances our existing fault injection software (OGSA-FIT) from the stateless environment of a standard web service to the stateful environment of an OGSA Toolkit (Globus). We compare our initial proof of concept experiment to our new target system based on the Globus Toolkit. The Globus Toolkit is implemented around an Apache Tomcat server using the Axis SOAP library as well as OGSA interfaces and libraries. We address issues arising from latencies introduced into the system by OGSA-FIT. We introduce a model for calculating this latency and introduce new mechanisms into the software to reduce this. We also present results from our initial experiments, which showed a problem with an alpha version of the Globus Toolkit. We detail future research including plans to enhance our user GUI to provide semi-automatic test campaign generation. Also since our OGSA-FIT software is intended to support both OGSA based middleware as well as standard SOAP based web-service environments we outline our research into providing interchangeable personality modules