This thesis investigates TCP connection management mechanisms in order to understand the behaviour and improve the performance of Internet servers during overload conditions such as flash crowds. We study several alternatives for implementing TCP connection establishment, reviewing approaches taken by existing TCP stacks as well as proposing new mechanisms to improve server throughput and reduce client response times under overload. We implement some of these connection establishment mechanisms in the Linux TCP stack and evaluate their performance in a variety of environments. We also evaluate the cost of supporting half-closed connections at the server and assess the impact of an abortive release of connections by clients on the throughput of an overloaded server. Our evaluation demonstrates that connection establishment mechanisms that eliminate the TCP-level retransmission of connection attempts by clients increase server throughput by up to 40% and reduce client response times by two orders of magnitude. Connection termination mechanisms that preclude support for half-closed connections additionally improve server throughput by up to 18%.

Web servers become overloaded when one or several server resources such as network interface, CPU and disk become overutilized. Server overload leads to low server throughput and long response times experienced by the clients. Traditional server design includes only marginal or no support for overload protection. This thesis presents the design, implementation and evaluation of architectures that provide overload protection and service differentiation in web servers. During server overload not all requests can be processed in a timely manner. Therefore, it is desirable to perform service differentiation, i.e., to service requests that are regarded as more important than others. Since requests that are eventually discarded also consume resources, admission control should be performed as early as possible in the lifetime of a web transaction. Depending on the workload, some server resources can be overutilized while the demand on other resources is low because certain types of requests utilize one resource more than others. The implementation of admission control in the kernel of the operating system shows that this approach is more efficient and scalable than implementing the same scheme in user space. We also present an admission control architecture that performs admission control based on the current server resource utilization combined with knowledge about resource consumption of requests. Experiments demonstrate more than 40% higher throughput during overload compared to a standard server and several magnitudes lower response times. This thesis also presents novel architectures and implementations of operating system support for predictable service guarantees. The Nemesis operating system provides applications with a guaranteed communication service using the developed TCP/IP implementation and the scheduling of server resources. SILK (Scout in the Linux kernel) is a new networking stack for the Linux operating system that is based on the Scout operating system. Experiments show that SILK enables prioritizing and other forms of service differentiation between network connections while running unmodified Linux applications.

Thesis (M.C.S.) - Carleton University, 2003. / Includes bibliographical references (p. 100-103). Also available in electronic format on the Internet.

Thesis (M.S.)--California Polytechnic State University, 2010. / Title from PDF title page; viewed on June 21, 2010. Major professor: Michael Haungs, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Computer Science." "June 2010." Includes bibliographical references (p. 76-77).

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 102-105). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 102-105). Also available on the Internet.

Dans cette thèse, nous nous intéressons au contrôle d’accès obligatoire dans les serveurs d’applications Web. Nous présentons une approche de protection obligatoire fondée sur un modèle abstrait d’applications Web. Les modèles d’applications Web existants, comme par exemple SOA peuvent être représentés par ce modèle abstrait d’application. Notre protection obligatoire s’appuie sur un langage de protection dédié permettant d’exprimer les besoins en terme de contrôle d’accès au sein d’un serveur d’application Web. Ce langage de protection utilise notre modèle d’application pour contrôler de manière efficace les accès des sujets aux objets de l’applications Web. Nous établissons également une méthode de calcul automatisé des politiques de sécurité qui facilite donc l’administration de la protection obligatoire proposée. Une implémentation sur des environnements Microsoft basés sur le serveur Web IIS et le canevas .Net est présentée. La solution est indépendante des applications Web protégées car elle repose sur l’utilisation d’un adaptateur applicatif pour s’interfacer avec n’importe quelle application. Celle-ci est fonctionnelle sur des environnements de workflow de la société QualNet ayant co-financée cette thèse. Les expérimentations menées montrent que notre protection obligatoire supporte des environnements à grande échelle et impose une élévation faible du temps de traitement, de l’ordre de 5%, qui diminue lorsque la taille des applications augmente. / This thesis focuses on mandatory access control in Web applications server. We present a novel approach of mandatory protection based on an abstract Web application model. Existing models of Web applications such as SOA fit with our abstract model. Our mandatory protection uses a dedicated language that allows to express the security requirements of a Web application. This dedicated protection language uses our Web application model to control efficiently the accesses of the subjects to the objects of a Web application. We establish a method to automatically compute the requested security policies facilitating thus the administration of the mandatory protection. An implementation on Microsoft-based environments uses the IIS Web server and the .Net Framework. The solution is independent from the Web applications to protect since it uses an application adaptor to interface our mandatory protection with the applications. This implementation is fully running on the workflow environments from the QualNet society, that cofunded this Ph.D thesis. Experiments show that our mandatory protection supports large scale environments since the overhead is near to 5 % and decreases when the size of the application increases.

Este trabalho propõe mecanismos de diferenciação de serviços para servidores Web, visando a melhorar o desempenho desses sistemas quando são consideradas as características das requisições Web nas políticas de atendimento. Optou-se por adotar o contexto do comércio eletrônico para a realização das pesquisas, uma vez que esse ambiente é um dos mais impactados negativamente quando há um comportamento inadequado do servidor em situações de sobrecarga. Para isso, foi realizada uma investigação das características das requisições Web típicas do e-commerce, para que tais características pudessem ser usadas como diretrizes para os mecanismos e melhorar o desempenho dos servidores. Em seguida, foram propostos um modelo de carga de trabalho e um modelo de simulação para a realização dos experimentos. Com isso, foi possível avaliar os resultados obtidos com a inserção dos diversos mecanismos no Servidor Web com Diferenciação de Serviços (SWDS), um modelo de servidor cuja arquitetura o torna capaz de fornecer serviços diferenciados a seus usuários e aplicações. Foram propostos novos mecanismos de escalonamento de requisições bem como novos mecanismos de controle de admissão. Diversas simulações foram realizadas e os resultados obtidos mostram que a exploração das características das requisições Web, além de ser fundamental para um bom entendimento do comportamento do servidor, possibilita a melhoria de desempenho do sistema / This work proposes differentiated services mechanisms for Web servers, aiming at improving their performance when the features of Web requests are considered. The electronic commerce (e-commerce) context was adopted to develop the researches once this environment is one of the most negatively influenced when there is an inadequate behavior of the server under overload situations. Thus, it was realized an investigation on the features of ecommerce Web requests, so that these features could be used both as guidelines for the mechanisms and to improve the performance of the servers. Afterwards, a workload model and a simulation model were proposed to implement the experiments. Thus, it was possible to evaluate the results obtained with the insertion of several mechanisms in the Web Server with Differentiated Services (WSDS), a server model with an architecture that makes it capable of supplying differentiated services to its users and applications. New request scheduling mechanisms were proposed as well as new mechanisms for admission control. Several simulations were realized and the obtained results show that the exploration of the Web request features, besides being fundamental for a good understanding of the server behavior, makes possible to improve the system performance

In today’s technology industry, cloud refers to servers which can be accessed viainternet, and the software and database applications run on the servers [22]. Whereas cloud computing is a concept of delivering the IT resources via internet which is accessed by the users and companies. In these scenarios OpenStack is the widely used cloud software which controls large pool of IT resources like compute, storage and networking which are managed and provisioned through APIs [11]. In this technology the underlying parts are the transport protocols and web servers used for authenticating and provisioning mechanisms. When stating about its underlying transport protocols, TCP is the default (standard) protocol used behind the functioning of cloud, and HTTP/1.1 version towards actions between Web servers (apache2 and nginx) and browsers [10]. The scope of the thesis is to observe the complexity of replacing TCP with QUIC (Quick UDP Internet Connection) in OpenStack and to observe the performance difference in OpenStack using HTTP/1.1 and HTTP/3. To observe this complexity, Performance Evaluation has been considered the best way in which the performance can be observed from the terminals. The thesis deals with performance of OpenStack with transport protocols from a Web server supporting HTTP/3 feature. We prove that its possible to provide the Keystone API via both HTTP/1.1 and HTTP/3. From our results we see that for simple API access HTTP/3 is faster than the HTTP/1.1 and also when the network is subjected to packet loss. The resultstates that there is a path obtained for OpenStack’s Keystone Service to interact with HTTP/3 and the average request-response time (total time) of HTTP/3 is less than that of HTTP/1.1 for accessing Keystone and Token generation even at defined packet loss rates.

[pt] Os desenvolvedores de sistemas cliente-servidor constantemente se deparam com questões de desempenho e escalabilidade, muitas vezes o número de clientes simultâneos de um servidor pode crescer de forma significativa. Além disso, se esses sistemas podem executar códigos de terceiros, passa a existir a preocupação com a questão de segurança da execução destes trechos de códigos. O objetivo desse trabalho é testar o desempenho de diversas combinações de modelos de concorrência e sandboxes. Como exemplo de sistema sujeito a solicitações concorrentes que precisa permitir a execução de programas de terceiros, temos os servidores web. O Xavante é um servidor web desenvolvido na linguagem de programação Lua que originalmente utiliza um modelo de programação concorrente baseado em co-rotinas. Esse servidor já possuía a flexibilidade de mapear tipos de requisição a tratadores diferentes. Alguns desses tratadores de requisi ção permitem a utilização de código de terceiros em tempo de execução e, por isso, já fazem uso de sandboxes a fim de oferecer um ambiente de execução protegido. Nesse trabalho testamos o uso dessas sandboxes nativas ao Xavante além de outros tipos de sandboxes. Também aumentamos as possibilidades de extensão do servidor, flexibilizando a arquitetura de modo a permitir diferentes estratégias de concorrência. Utilizando a nova arquitetura testamos o desempenho das diversas combinações de sandboxes e modelos de programação concorrente, permitindo a comparação dos modelos não só do ponto de vista qualitativo mas também medindo o impacto de desempenho do seu uso. / [en] Client-server developers constantly have to deal with questions concerning performance and scalability, since the number of simultaneous clients can grow significantly. Moreover, if these systems can execute third-party code, there is also the concern of secure execution of these pieces of code. This work goal is to benchmark several combinations of concurrency and sandboxes models. As an example of a system exposed to several concurrent requests that must be able to execute third-party code, we have the web servers. Xavante is a web server developed in the Lua programming language that originally uses an concurrency programming model based on coroutines. This server offers the flexibility to map request types to different handlers. Some of these request handlers dynamically allow the use of third-party code, therefore they make use of sandboxes in order to offer a protected running environment. In this work we test the use of Xavante´s native sandboxes and other types of sandboxes.We also improve the extensibility of the server, using a different architecture in order to allow different concurrency strategies. Using the new architecture we tested the performance of several combinations of sandboxes and concurrency programming models, allowing the model comparison not only in a qualitative point of view but also measuring the related performance impacts.