Revisiting Client/Server Computing

The role of the Information Technology department is changing as it continues to mature and adapt to changes in technology, much of that change dealing with its interaction with corporate end-users. IT departments must continue to move in a more user friendly direction or they are going to encounter serious political problems with top management. The increased interest in cloud computing, green computing, and in outsourcing are further indicators of the problems that IT departments are currently facing.   Information Technology departments must approach client/server with a clear view of the lasting business benefits that it can bring rather than opposing or resisting the migratio

Swiftmend: Data Synchronization in Open mHealth Applications with Restricted Connectivity

Open mHealth applications often include mobile devices and cloud services with replicated data between components. These replicas need periodical synchronization to remain consistent. However, there are no guarantee of connectivity to networks which do not bill users on the quantity of data usage. This thesis propose Swiftmend, a system with synchronization that minimize the quantity of I/O used on the network. Swiftmend includes two reconciliation algorithms; Rejuvenation and Regrowth. The latter utilizes the efficiency of the Merkle tree data structure to reduce the I/O. Merkle trees can sum up the consistency of replicas into compact fingerprints. While the first reconciliation algorithm, Rejuvenation simply inspects the entire replica to identify consistency. Regrowth is shown to produce less quantity of I/O than Rejuvenation when synchronizing replicas. This is due to the compact fingerprints

Managing IT Operations in a Cloud-driven Enterprise: Case Studies

Enterprise IT needs a new approach to manage processes, applications and infrastructure which are distributed across a mix of environments. In an Enterprise traditionally a request to deliver an application to business could take weeks or months due to decision-making functions, multiple approval bodies and processes that exist within IT departments. These delays in delivering a requested service can lead to dissatisfaction, with the result that the line-of-business group may seek alternative sources of IT capabilities. Also the complex IT infrastructure of these enterprises cannot keep up with the demand of new applications and services from an increasingly dispersed and mobile workforce which results in slower rollout of critical applications and services, limited resources, poor operation visibility and control. In such scenarios, it’s better to adopt cloud services to substitute for new application deployment otherwise most Enterprise IT organizations face the risk of losing 'market share' to the Public Cloud. Using Cloud Model the organizations should increase ROI, lower TCO and operate with seamless IT operations. It also helps to beat shadow IT and the practice of resource over-or under provisioning. In this research paper we have given two case studies where we migrated two Enterprise IT application to public clouds for the purpose of lower TCO and higher ROI. By migrating, the IT organizations improved IT agility, enterprise-class software for performance, security and control. In this paper, we also focus on the advantages and challenges while adopting cloud services

A Holistic Approach to Lowering Latency in Geo-distributed Web Applications

User perceived end-to-end latency of web applications have a huge impact on the revenue for many businesses. The end-to-end latency of web applications is impacted by: (i) User to Application server (front-end) latency which includes downloading and parsing web pages, retrieving further objects requested by javascript executions; and (ii) Application and storage server(back-end) latency which includes retrieving meta-data required for an initial rendering, and subsequent content based on user actions. Improving the user-perceived performance of web applications is challenging, given their complex operating environments involving user-facing web servers, content distribution network (CDN) servers, multi-tiered application servers, and storage servers. Further, the application and storage servers are often deployed on multi-tenant cloud platforms that show high performance variability. While many novel approaches like SPDY and geo-replicated datastores have been developed to improve their performance, many of these solutions are specific to certain layers, and may have different impact on user-perceived performance. The primary goal of this thesis is to address the above challenges in a holistic manner, focusing specifically on improving the end-to-end latency of geo-distributed multi-tiered web applications. This thesis makes the following contributions: (i) First, it reduces user-facing latency by helping CDNs identify and map objects that are more critical for page-load latency to the faster CDN cache layers. Through controlled experiments on real-world web pages, we show the potential of our approach to reduce hundreds of milliseconds in latency without affecting overall CDN miss rates. (ii) Next, it reduces back-end latency by optimally adapting the datastore replication policies (including number and location of replicas) to the heterogeneity in workloads. We show the benefits of our replication models using real-world traces of Twitter, Wikipedia and Gowalla on a 8 datacenter Cassandra cluster deployed on EC2. (iii) Finally, it makes multi-tier applications resilient to the inherent performance variability in the cloud through fine-grained request redirection. We highlight the benefits of our approach by deploying three real-world applications on commercial cloud platforms

Resource management of replicated service systems provisioned in the cloud

Service providers seek scalable and cost-effective cloud solutions for hosting their applications. Despite significant recent advances facilitating the deployment and management of services on cloud platforms, a number of challenges still remain. Service providers are confronted with time-varying requests for the provided applications, inter- dependencies between different components, performance variability of the procured virtual resources, and cost structures that differ from conventional data centers. Moreover, fulfilling service level agreements, such as the throughput and response time percentiles, becomes of paramount importance for ensuring business advantages.In this thesis, we explore service provisioning in clouds from multiple points of view. The aim is to best provide service replicas in the form of VMs to various service applications, such that their tail throughput and tail response times, as well as resource utilization, meet the service level agreements in the most cost effective manner. In particular, we develop models, algorithms and replication strategies that consider multi-tier composed services provisioned in clouds. We also investigate how a service provider can opportunistically take advantage of observed performance variability in the cloud. Finally, we provide means of guaranteeing tail throughput and response times in the face of performance variability of VMs, using Markov chain modeling and large deviation theory. We employ methods from analytical modeling, event-driven simulations and experiments. Overall, this thesis provides not only a multi-faceted approach to exploring several crucial aspects of hosting services in clouds, i.e., cost, tail throughput, and tail response times, but our proposed resource management strategies are also rigorously validated via trace-driven simulation and extensive experiment

Scalable hosting of web applications

Modern Web sites have evolved from simple monolithic systems to complex multitiered systems. In contrast to traditional Web sites, these sites do not simply deliver pre-written content but dynamically generate content using (one or more) multi-tiered Web applications. In this thesis, we addressed the question: How to host multi-tiered Web applications in a scalable manner? Scaling up a Web application requires scaling its individual tiers. To this end, various research works have proposed techniques that employ replication or caching solutions at different tiers. However, most of these techniques aim to optimize the performance of individual tiers and not the entire application. A key observation made in our research is that there exists no elixir technique that performs the best for allWeb applications. Effective hosting of a Web application requires careful selection and deployment of several techniques at different tiers. To this end, we present several caching and replication strategies, such as GlobeCBC, GlobeDB and GlobeTP, to improve the scalability of different tiers of a Web application. While these techniques and systems improve the performance of the individual tiers (and eventually the application), an application's administrator is not only interested in the performance of its individual tiers but also in its endto- end performance. To this end, we propose a resource provisioning approach that allows us to choose the best resource configuration for hosting a Web application such that its end-to-end response time can be optimized with minimum usage of resources. The proposed approach is based on an analytical model for multi-tier systems, which allows us to derive expressions for estimating the mean end-to-end response time and its variance.Steen, M.R. van [Promotor]Pierre, G.E.O. [Copromotor

A Comparison of wide area network performance using virtualized and non-virtualized client architectures

The goal of this thesis is to determine if there is a significant performance difference between two network computer architecture models. The study will measure latency and throughput for both client-server and virtualized client architectures. In the client server environment, the client computer performs a significant portion of the work and frequently requires downloading uploading files to and from a remote location. Virtual client architecture turns the client machine into a terminal, sending only keystrokes and mouse clicks and receiving only display pixel or sound changes. I accomplished the goal of comparing these architectures by comparing completion times for ping reply, file download, a small set of common work tasks, and a moderately large SQL database query. I compared these tasks using simulated wide area network, local area network, and virtual client network architectures. The study limits the architecture to one where the virtual client and server are in the same data center

Design and Evaluation of Distributed Algorithms for Placement of Network Services

Network services play an important role in the Internet today. They serve as data caches for websites, servers for multiplayer games and relay nodes for Voice over IP: VoIP) conversations. While much research has focused on the design of such services, little attention has been focused on their actual placement. This placement can impact the quality of the service, especially if low latency is a requirement. These services can be located on nodes in the network itself, making these nodes supernodes. Typically supernodes are selected in either a proprietary or ad hoc fashion, where a study of this placement is either unavailable or unnecessary. Previous research dealt with the only pieces of the problem, such as finding the location of caches for a static topology, or selecting better routes for relays in VoIP. However, a comprehensive solution is needed for dynamic applications such as multiplayer games or P2P VoIP services. These applications adapt quickly and need solutions based on the immediate demands of the network. In this thesis we develop distributed algorithms to assign nodes the role of a supernode. This research first builds off of prior work by modifying an existing assignment algorithm and implementing it in a distributed system called Supernode Placement in Overlay Topologies: SPOT). New algorithms are developed to assign nodes the supernode role. These algorithms are then evaluated in SPOT to demonstrate improved SN assignment and scalability. Through a series of simulation, emulation, and experimentation insight is gained into the critical issues associated with allocating resources to perform the role of supernodes. Our contributions include distributed algorithms to assign nodes as supernodes, an open source fully functional distributed supernode allocation system, an evaluation of the system in diverse networking environments, and a simulator called SPOTsim which demonstrates the scalability of the system to thousands of nodes. An example of an application deploying such a system is also presented along with the empirical results

Reducing the Tail Latency of a Distributed NoSQL Database

The request latency is an important performance metric of a distributed database, such as the popular Apache Cassandra, because of its direct impact on the user experience. Specifically, the latency of a read or write request is defined as the total time interval from the instant when a user makes the request to the instant when the user receives the request, and it involves not only the actual read or write time at a specific database node, but also various types of latency introduced by the distributed mechanism of the database. Most of the current work focuses only on reducing the average request latency, but not on reducing the tail request latency that has a significant and severe impact on some of database users. In this thesis, we investigate the important factors on the tail request latency of Apache Cassandra, then propose two novel methods to greatly reduce the tail request latency. First, we find that the background activities may considerably increase the local latency of a replica and then the overall request latency of the whole database, and thus we propose a novel method to select the optimal replica by considering the impact of background activities. Second, we find that the asynchronous read and write architecture handles the local and remote requests in the same way, which is simple to implement but at a cost of possibly longer latency, and thus we propose a synchronous method to handle local and remote request differently to greatly reduce the latency. Finally, our experiments on Amazon EC2 public cloud platform demonstrate that our proposed methods can greatly reduce the tail latency of read and write requests of Apache Cassandra. Adviser: Dr. Lisong X