CLIENT-SIDE EVALUATION OF QUALITY OF SERVICE IN CLOUD APPLICATIONS

Cloud computing is a constantly developing topic that reaches most of the people in the world on a daily basis. Almost every website and mobile application is hosted through a cloud provider. Two of the most important metrics for customers is performance and availability. Current tools that mea- sure availability are using the Internet Control Message Protocol (ICMP) to monitor availability, which has shown to be unreliable. This thesis suggests a new way of monitoring both availability and response time by using Hypertext Transfer Protocol (HTTP). Through HTTP, we are able to reach both the front-end of the cloud service (just as ICMP), but also deeper, to find failures in the back-end, that ICMP would miss. With our monitoring tool, we have monitored five different cloud data centers during one week. We found that cloud providers are not always keeping their promised SLA and it might be up to the cloud customers to reach a higher availability. We also perform load tests to analyze how vertical and horizontal scaling performs with regards to response time. Our analysis concludes that, at this time, vertical scaling outperforms horizontal scaling when it comes to response time. Even when this is the case, we suggest that developers should build applications that are horizontally scalable. With a horizontally scalable application and our monitoring tool combined, we can reach higher availability than is currently possible.