Due to their loosely coupled and highly dynamic nature, service-oriented systems offer many benefits for realizing fault tolerance and supporting trustworthy computing. They enable automatic system reconfiguration when a faulty service is detected. Spectrum-based fault localization (SFL) is a statistics-based diagnosis technique that can be effectively applied to pinpoint problematic services. However, SFL exhibits poor performance in diagnosing services which are tightly interacted. Previous research suggests that an increase in the number of monitoring locations may improve the diagnosability for tight interaction. In this paper, we analyze the trade-offs between the diagnosis improvement through increased monitoring granularity and the overhead caused by the introduction of more monitors, when diagnosing tightly interacted faulty services. We apply SFL in a service-based system, for which we show that 100 % correct identification of faulty services can be achieved through the increased monitoring granularity. We assess the overhead with increased monitoring granularity and compare this with the original monitoring setup. Our experimental results show that the monitoring at the service communication level causes relatively high overhead, whereas the monitoring overhead at a finer level of granularity, i.e., at the service implementation level, is much lower, but highly dependent on the number of monitors deployed.

Web APIs provide a systematic and extensible approach for application-to-application interaction. Developers using web APIs are forced to accompany the API providers in their software evolution tasks. In order to understand the distress caused by this imposition on web API client developers we perform a semi-structured interview with six such developers. We also investigate how major web API providers organize their API evolution, and we explore how this affects source code changes of their clients. Our exploratory qualitative study of the Twitter, Google Maps, Facebook and Netflix web APIs analyzes the state of web API evolution practices and provides insight into the impact of service evolution on client software. In order to complement the picture and also understand how web API providers deal with evolution, we investigate the server-side and client-side evolution of two open-source web APIs, namely VirtualBox and XBMC. Our study is complemented with a set of observations regarding best practices for web API evolution.