Linear Scalability of Distributed Applications

The explosion of social applications such as Facebook, LinkedIn and Twitter, of electronic commerce with companies like Amazon.com and Ebay.com, and of Internet search has created the need for new technologies and appropriate systems to manage effectively a considerable amount of data and users. These applications must run continuously every day of the year and must be capable of surviving sudden and abrupt load increases as well as all kinds of software, hardware, human and organizational failures. Increasing (or decreasing) the allocated resources of a distributed application in an elastic and scalable manner, while satisfying requirements on availability and performance in a cost-effective way, is essential for the commercial viability but it poses great challenges in today's infrastructures. Indeed, Cloud Computing can provide resources on demand: it now becomes easy to start dozens of servers in parallel (computational resources) or to store a huge amount of data (storage resources), even for a very limited period, paying only for the resources consumed. However, these complex infrastructures consisting of heterogeneous and low-cost resources are failure-prone. Also, although cloud resources are deemed to be virtually unlimited, only adequate resource management and demand multiplexing can meet customer requirements and avoid performance deteriorations. In this thesis, we deal with adaptive management of cloud resources under specific application requirements. First, in the intra-cloud environment, we address the problem of cloud storage resource management with availability guarantees and find the optimal resource allocation in a decentralized way by means of a virtual economy. Data replicas migrate, replicate or delete themselves according to their economic fitness. Our approach responds effectively to sudden load increases or failures and makes best use of the geographical distance between nodes to improve application-specific data availability. We then propose a decentralized approach for adaptive management of computational resources for applications requiring high availability and performance guarantees under load spikes, sudden failures or cloud resource updates. Our approach involves a virtual economy among service components (similar to the one among data replicas) and an innovative cascading scheme for setting up the performance goals of individual components so as to meet the overall application requirements. Our approach manages to meet application requirements with the minimum resources, by allocating new ones or releasing redundant ones. Finally, as cloud storage vendors offer online services at different rates, which can vary widely due to second-degree price discrimination, we present an inter-cloud storage resource allocation method to aggregate resources from different storage vendors and provide to the user a system which guarantees the best rate to host and serve its data, while satisfying the user requirements on availability, durability, latency, etc. Our system continuously optimizes the placement of data according to its type and usage pattern, and minimizes migration costs from one provider to another, thereby avoiding vendor lock-in.

Autonomic SLA-driven Provisioning for Cloud Applications

Karl Aberer, Nicolas Bonvin

Significant achievements have been made for automated allocation of cloud resources. However, the performance of applications may be poor in peak load periods, unless their cloud resources are dynamically adjusted. Moreover, although cloud resources dedicated to different applications are virtually isolated, performance fluctuations do occur because of resource sharing, and software or hardware failures (e.g. unstable virtual machines, power outages, etc.). In this paper, we propose a decentralized economic approach for dynamically adapting the cloud resources of various applications, so as to statistically meet their SLA performance and availability goals in the presence of varying loads or failures. According to our approach, the dynamic economic fitness of a Web service determines whether it is replicated or migrated to another server, or deleted. The economic fitness of a Web service depends on its individual performance constraints, its load, and the utilization of the resources where it resides. Cascading performance objectives are dynamically calculated for individual tasks in the application workflow according to the user requirements. By fully implementing our framework, we experimentally proved that our adaptive approach statistically meets the performance objectives under peak load periods or failures, as opposed to static resource settings.

2011

Optimal application-oriented resource brokering in a high performance computing grid

Vincent Keller

In the world of High Performance Computing (newly renamed "High Productivity Computing"), where the race for performance is on, where the hunt for the last Flop rages and where the developers swear by the Cult of Power, the different applications have different needs. Some of them are single threaded, others are parallel, some are memory bandwidth, others processor speed dominated. Some are embarrassingly parallel, point-to-point or multicast dominated, all depending on the algorithms and numerical methods they implement. Computing resources are also different, some are low-cost clusters of PlayStations 3, clusters with more or less efficient networks, others are expensive vector supercomputers. To express that diversity, a parameterization of the applications and the resources is proposed. Based on this parameterization, it is possible to quantify the needs of the different types of applications in terms of memory, processor and network requirements. On the other hand, the parameterization of the resources quantifies what a resource "offers" in term of memory, processor or network performance. Comparing the needs of the application and the offers of the resources, we present a model that predicts the computation and the communication times, and consequently the execution times of an application on different resources. We define a cost model that finds the best matches between an application and the available resources in an HPC Grid. It takes into account the cost of execution time of the application (based on the prediction previously mentioned), the waiting time cost (based on the information given by the local resource management systems), the cost of the licenses of the different software the application may use, the cost of the data transfer, and the ecological cost. The choice is made on a QOS (Quality of Service) given by the user, such as minimum turnaround time or minimum cost. Computing these different costs requires a fine knowledge of the behavior of the application on the resource. Thus we present a detailed application-oriented monitoring that consists in mapping information from the hardware monitoring and the different middleware the application (or the resource) uses, such as MPI detailed information, the hardware counters or the information of the execution on a local resource management system. The monitored data is stored in an archive system. The archived monitoring data concerning the behavior of the applications on the different resources, can then be used to help deciders purchasing new best suited resources for the current (and future) applications. In the second part of this work, we go further in matching the applications and resources: if it is possible to predict the behavior of an application on a given resource, it is also possible to fit the resource to the needs of the application. Knowing the processor performance needs of the application during its execution, it is possible to adjust its frequency through the frequency stepping mechanism that authorizes an operating system kernel or a program to modify on the fly the frequency (and the voltage) of the present days processors. Hence the resource exactly fits the needs of the application and the energy consumption of the processor is reduced. Finally, we propose a methodology to determine poorly implemented applications and thus giving users and developers hints and advice to detect flaws in an automatic manner. We present a real-life example, a spectral element code in CFD, for which the complexity changed when more than 1024 processors were used.

EPFL2008

An economic approach for scalable and highly-available distributed applications

Karl Aberer, Nicolas Bonvin

Service-oriented architecture (SOA) paradigm for orchestrating large-scale distributed applications offers significant cost savings by reusing existing services. However, the high irregularity of client requests and the distributed nature of the approach may deteriorate service response time and availability. Static replication of components in datacenters for accommodating load spikes requires proper resource planning and underutilizes the cloud infrastructure. Moreover, no service availability guarantees are offered in case of datacenter failures. In this paper, we propose a cost-efficient approach for dynamic and geographically diverse replication of components in a cloud computing infrastructure that effectively adapts to load variations and offers service availability guarantees. In our virtual economy, service components rent server resources and replicate, migrate or delete themselves according to self-optimizing strategies. We experimentally prove that such an approach outperforms even full replication of the components in all servers with respect to response time, while offering service availability guarantees under failures.

2010

Optimal application-oriented resource brokering in a high performance computing grid

Vincent Keller

EPFL2008