A Trust Evaluation Method for Cloud Service with Fluctuant QoS and Flexible SLA

The QoS (quality of service) of a cloud service is not always trusted as advertised, due to the variable network environment or fake advertisement reasons. Therefore, to promote the trusted service selection, we should first evaluate the trust of each cloud service, based on its historical QoS records from past invocations. However, different from the traditional web service whose historical QoS record is a fixed value (e.g., a historical latency record of a web service is 2s), the historical QoS record of a cloud service is usually not fixed, but fluctuant during the long-running period of a single service invocation. For example, an virtual organization O rents cloud service WeatherInquiry between 8:00 am and 8:00 pm so that the employees of O can access WeatherInquiry. In this scenario, the latency of WeatherInquiry is fluctuant from the perspective of organization O, during the served 12 hours. In this situation, it is a challenge to evaluate the trust of service WeatherInquiry, based on WeatherInquiry's multiple historical QoS records that fluctuate continuously. In view of this challenge, we introduce a novel concept of flexible SLA, to better accommodate the fluctuant QoS of cloud service, and further put forward a trust evaluation method based on fluctuant QoS and flexible SLA, i.e., FL-FL (FLuctuant QoS-FLexible SLA-based trust evaluation method, FL-FL). Finally, a set of experiments are designed and deployed to validate the feasibility of our proposal, in terms of effectiveness and efficiency.