Sasko Ristov

Architecture and organization of e-Assessment cloud solution

All e-Assessment systems have several challenges, such as accurate evaluation, security and data privacy, performance, scalability etc. In this paper we focus on e-Assessment scalability and performance. We propose a SOA architecture of a cloud hosted e-Assessment system which uses scalability and elasticity in order to achieve sustainable performance. Our solution consists of three subsystems, the first for management, the second for reports, and the third for on-demand activities during the assessments. It reduces the overall costs since it uses minimum resources utilized only during the e-Assessment. Better performance is expected to be achieved since the active subsystem for each assessment works with much smaller data compared to the centralized one.

Compute and Memory Intensive Web Service Performance in the Cloud

Migration of web services from company’s on-site premises to cloud provides ability to exploit flexible, scalable and dynamic resources payable per usage and therefore it lowers the overall IT costs. However, additional layer that virtualization adds in the cloud decreases the performance of the web services. Our goal is to test the performance of compute and memory intensive web services on both on-premises and cloud environments. We perform a series of experiments to analyze the web services performance and compare what is the level of degradation if the web services are migrating from on-premises to cloud using the same hardware resources. The results show that there is a performance degradation on cloud for each test performed varying the server load by changing the message size and the number of concurrent messages. The cloud decreases the performance to 71.10% of on-premise for memory demand and to 73.86% for both memory demand and compute intensive web services. The cloud achieves smaller performance degradation for greater message sizes using the memory demand web service, and also for greater message sizes and smaller number of concurrent messages for both memory demand and compute intensive web services.

Superlinear speedup in Windows Azure cloud

Azure cloud offers Platform-as-a-Service (PaaS) to its customers. It uses Hyper-V hypervisor to manage instances of virtual machines. Several papers report superlinear speedup for execution of dense matrix-matrix multiplication algorithm comparing the parallel and sequential executions. The existence of a superlinear speedup is also confirmed in some cases of virtualized and cloud environments. In this paper we realized a series of experiments to find out if the superlinear speedup is also possible on the Azure cloud for executing the dense matrix-matrix multiplication algorithm using the same hardware infrastructure. In addition to the hypothesis about existence of a superlinear speedup we will theoretically explain the experimental results and determine the regions and particular matrix sizes where it may occur.

A superlinear speedup region for matrix multiplication

The realization of modern processors is based on a multicore architecture with increasing number of cores per processor. Multicore processors are often designed such that some level of the cache hierarchy is shared among cores. Usually, last level cache is shared among several or all cores (e.g., L3 cache) and each core possesses private low level caches (e.g., L1 and L2 caches). Superlinear speedup is possible for matrix multiplication algorithm executed in a shared memory multiprocessor due to the existence of a superlinear region. It is a region where cache requirements for matrix storage of the sequential execution incur more cache misses than in parallel execution. This paper shows theoretically and experimentally that there is a region, where the superlinear speedup can be achieved. We provide a theoretical proof of existence of a superlinear speedup and determine boundaries of the region where it can be achieved. The experiments confirm our theoretical results. Therefore, these results will have impact on future software development and exploitation of parallel hardware on the basis of a shared memory multiprocessor architecture. Copyright

Security evaluation of open source clouds

In this paper we analyze most common open source cloud architectures. We installed OpenStack, Eucalyptus, Open-Nebula, and CloudStack and evaluated the security aspects of their architecture and their compliance with security requirements defined by the ISO 27001:2005 standard which specifies the requirements for establishing, implementing, operating, monitoring, reviewing, maintaining and improving a documented Information Security Management System within the context of the organizations overall business risks. Although the analyzed open source cloud solutions offer scalable and flexible platforms for IaaS and provide a lot of security measures, still our research results show security incompliance with several ISO 27001:2005 controls and control objectives that directly depend on cloud software solutions.

Superlinear speedup for matrix multiplication

Amdahl has shown that multiprocessor execution performance is not proportional to the number of processors. Gustafson has found a way to show that there are algorithms which can have almost linear speedup. In this article we have found algorithms which can achieve a superlinear speedup. The idea is not based on changing the algorithm or executing smaller number of operations like in the parallel search. It is based on characteristics of using an structure persistent algorithm which efficiently exploits the cache in a shared multiprocessor and avoids cache misses as much as possible. Our experimental research shows results of superlinear speedup for algorithms which run on modern multicore and multi-chip architectures and perform beyond expectations of maximum linear speedup.

E-Assessment with interactive images

Besides the fact that e-Assessment systems can efficiently conduct all paper based tests to evaluate knowledge and skills, they can offer a lot of new features via sophisticated information and communication technologies, including adaptive testing, immediate evaluation, etc. Most of the realised e-Assessment systems use pictures in the realisation of e-Testing, but the pictures are mainly used as supported media enhancement of the multiple choice questions. We introduce a brand new idea to use interactive images, where the user can navigate and zoom the picture and provide answers by clicking on an appropriate graphical object, mark a region, annotate, set an answer/comment on a given position, etc. The application domain of this innovation is huge, including e-Assessment for those sciences, where image analysis is essential, such as analysis of medical images, gathering map selective users opinion etc. We have developed three new question types based on interactive images that offer these innovations. The impact is not just in enhancement of offered technology, but also on preventing various cheating methods, such as memorising, guessing, etc. These innovations can improve the assessment results, by a more correct evaluation and knowledge assessment.

Security Vulnerability Assessment of OpenStack Cloud

Migrating the virtual machines from on-premise to cloud raises new security challenges for a company. A potential threat to the tenants are not only the Internet hackers, but also the cloud service provider and the other co-tenants, due to the multi-tenancy feature. The cloud service providers security is challenged by the tenants, as well. Deploying the open source cloud raises additional challenges since the intruders have access to the cloud source code and can assess its vulnerabilities. In this paper, we thoroughly assess the security vulnerabilities of OpenStack cloud framework, one of the most used open source cloud frameworks today. We assess the vulnerabilities of OpenStack server node, virtual machine instances and OpenStacks Dashboard, the web management interface. The security assessment shows that OpenStack cloud has security vulnerabilities that need to be secured by developing the patch.

Optimal Resource Allocation to Host Web Services in Cloud

In this paper, we analyze the performance of computation intensive and memory demanding web services hosted in different environments with the same amount of resources, but orchestrated differently. A single-VM addresses the environment where all the resources are allocated in one huge virtual machine instance (VMI), while a multi-VM environment uses several smaller VMIs, each allocated with only one CPU core, and the load is balanced among them. We realize series of experiments with different server loads by changing the message size and the number of concurrent messages to analyze the optimal resource allocation to host web services in order to achieve maximum performance from the same resources in the cloud, i.e., for the same price. Despite the hypothesis that the single-VM environment provides better performance than the multi-VM environment, the results show totally opposite for almost all test cases. We achieve maximal relative speedup of 9.83 comparing the multi-VM environment to the single-VM.

Security vulnerabilities from inside and outside the Eucalyptus cloud

Cloud security becomes a hot topic in the emerging new cloud environments. Customers would like to understand what happens when they move their applications, data and information on the cloud. Probably one of the most interesting questions is what are the new challenges that cloud virtual environment produces due to multitenancy and virtualization. Security challenges addressed in this paper are vulnerabilities that may happen inside or outside the cloud environment. The security evaluation methodology uses Nessus scoring system for two target groups: physical and software parts using different scenarios. Our experiments are realized with four virtual machine instances instantiated in Eucalyptus cloud with different operating systems hosted. We also evaluate the security of the Eucalyptus cloud version.