This work introduces a novel approach for online design and execution of load tests on Cloud applications. Our approach utilizes a Combinatorial Test Design (CTD) engine in order to exercise combinations of levels of resource utilization on the target system's subcomponents. In order to cope with the unpredictability and uncontrollability of Cloud environments, and to align with agile and DevOps paradigms, it designs and executes tests in an iterative online fashion. During test execution, monitoring information is collected from the Cloud, and leveraged for driving and adjusting the subsequent test scenarios. In this work we introduce the overall approach and the algorithms behind it, and demonstrate it on an example setting consisting of three sub-components comprising a typical installation of a web blogging application.