The success of the cloud computing paradigm is due to its on-demand, self-service, and pay-by-use nature. According to this paradigm, the effects of Denial of Service (DoS) attacks involve not only the quality of the delivered service, but also the service maintenance costs in terms of resource consumption. Specifically, the longer the detection delay is, the higher the costs to be incurred. Therefore, a particular attention has to be paid for stealthy DoS attacks. They aim at minimizing their visibility, and at the same time, they can be as harmful as the brute-force attacks. They are sophisticated attacks tailored to leverage the worst-case performance of the target system through specific periodic, pulsing, and low-rate traffic patterns. In this paper, we propose a strategy to orchestrate stealthy attack patterns, which exhibit a slowly-increasing-intensity trend designed to inflict the maximum financial cost to the cloud customer, while respecting the job size and the service arrival rate imposed by the detection mechanisms. We describe both how to apply the proposed strategy, and its effects on the target system deployed in the cloud.

The diversity of Cloud computing services is challenging the application developers as various and non-standard interfaces are provided for these services. Few middleware solutions were developed until now to support the design, deployment and execution of service-independent applications as well as the management of resources from multiple Clouds. This paper focuses on one of these advanced middleware solutions, called mOSAIC. Written after the completion of its development, this paper presents an integrated overview of the mOSAIC approach and the use of its various software prototypes in a Cloud application development process. We are starting from the design concepts and arrive to various applications, as well as to the position versus similar initiatives.

The cloud paradigm appeared on the computing scene in 2005 with the Amazon Elastic Compute Cloud (EC2). After this date, a large set of related technologies has been developed. In the academic world, and especially in the HPC area, cloud computing is in some way in competition with the GRID model, which offers a middleware based approach. One of the solutions proposed is the integration of the two paradigms, in order to use the enormous potential of the existent computational GRIDs in new ways. One of the most diffused problems on this systems is the choice of the correct programming paradigm: many different approaches exist and it is difficult to define which is the approach that best fit with the cloud paradigm. In this paper we propose the integration of a Cloud on GRID architecture with a mobile agent platform. The architecture we propose offer Virtual clusters with full administrative control to final users, adopting an existent GRID architecture and especially its security infrastructure. The mobile agent platform is able to dynamically add and configure services on the virtual clusters. The experience here presented shows that the mobile agent paradigm well fulfills the dynamic properties of the Cloud paradigm and could be a good choice to simply develop application and services able to dynamically adapt themselves to the virtualized environment.