Improving resource provisioning of heterogeneous cloud infrastructures is an important research challenge. The wide diversity of cloud-based applications and customers with different QoS requirements have recently exhibited the weaknesses of current provisioning systems. Today's cloud infrastructures provide provisioning systems that dynamically adapt the computational power of applications by adding or releasing resources. Unfortunately, these scaling systems are fairly limited: (i) They restrict themselves to a single type of resource; (ii) they are unable to fulfill QoS requirements in face of spiky workload; and (iii) they offer the same QoS level to all their customers, independent of customer preferences such as different levels of service availability and performance. In this paper, we present an autoscaling system that overcomes these limitations by exploiting heterogeneous types of resources, and by defining multiple levels of QoS requirements. The proposed system selects a resource scaling plan according to both workload and customer requirements. Our experiments conducted on both public and private infrastructures show significant reductions in QoS-level violations when faced with highly variable workloads.
Background. Energy efficiency is an increasingly important property of software. A large number of empirical studies have been conducted on the topic. However, current state-of-the-Art does not provide empiricallyvalidated guidelines for developing energy-efficient software. Aim. This study aims at assessing the impact, in terms of energy savings, of best practices for achieving software energy efficiency, elicited from previous work. By doing so, it identifies which resources are affected by the practices and the possible trade-offs with energy consumption. Method. We performed an empirical experiment in a controlled environment, where we applied two different Green Software practices to two software applications, namely query optimization in MySQL Server and usage of "sleep" instruction in the Apache web server. We then performed a comparison of the energy consumption at system-level and at resource-level, before and after applying the practice. Results. Our results show that both practices are effective in improving software energy efficiency, reducing consumption up to 25%. We observe that after applying the practices, resource usage is more energy-proportional i.e. increasing CPU usage increases energy consumption in an almost linear way. We also provide our reflections on empirical experimentation in software energy efficiency. Conclusions. Our contribution shows that significant improvements in software energy efficiency can be gained by applying best practices during design * Corresponding author Email addresses: g.procaccianti@vu.nl (Giuseppe Procaccianti), hector.fernandez@vu.nl (Hector Fernandez), p.lago@vu.nl (Patricia Lago)Preprint accepted for publication in Journal of Systems and Software February 24, 2016 and development. Future work will be devoted to further validate best practices, and to improve their reusability.
Nowadays, executions of composite Web services are typically conducted by heavyweight centralized workflow engines. This represents a potential processing and communication bottleneck as well as a single point of failure. In addition to this, centralization induces higher deployment costs, such as a computing infrastructure to support the workflow engine, which is not affordable for a large number of small businesses and end-users. Last but not least, a central workflow engine might expose some security risks such as the business process discovery. More decentralized and dynamic interaction schemes are thus required.In this paper, we propose a decentralized alternative system for the execution of composite Web services based on an unconventional programming paradigm that relies on the chemical metaphor. It provides a high-level execution model that allows executing composite services in a fully decentralized manner. Our architecture is composed of nodes communicating through a persistent and fault-tolerant shared space containing both control and data flows, allowing to distribute the composition among nodes without the need for any centralized coordination.
International audienceWith the recent widespread adoption of service-oriented architecture, the dynamic composition of services is now a crucial issue in the area of distributed computing. The coordination and execution of composite Web services are today typically conducted by heavyweight centralized workflow engines, leading to an increasing probability of processing and communication bottlenecks and failures. In addition, centralization induces higher deployment costs, such as the computing infrastructure to support the workflow engine, which is not affordable for a large number of small businesses and end-users. In a world where platforms are more and more dynamic and elastic as promised by cloud computing, decentralized and dynamic interaction schemes are required. Addressing the characteristics of such platforms, nature-inspired analogies recently regained attention to provide autonomous service coordination on top of dynamic large scale platforms. In this paper, we propose an approach for the decentralized execution of composite Web services based on an unconventional programming paradigm that relies on the chemical metaphor. It provides a high-level execution model that allows executing composite services in a decentralized manner. Composed of services communicating through a persistent shared space containing control and data flows between services, our architecture allows to distribute the composition coordination among nodes. A proof of concept is given, through the deployment of a software prototype implementing these concepts, showing the viability of an autonomic vision of service composition
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