Replicated Web Servers Research Articles

Web-server dynamic load balancing system

Usage of Internet and frequent accesses of large amount of multimedia data increase the network traffic. Performance evaluation and high availability of server are important factors for resolving this problem using cluster based systems. There are several low-cost servers using the load sharing cluster system which are connected to high speed network, and apply load balancing technique between servers. It offers high computing power and high availability. The overall increase in traffic on the World Wide Web is augmenting user-perceived response times from popular Web sites, especially in conjunction with special events. A distributed website server can provide scalability and flexibility to manage with growing client demands. To improve the response time of the web server, the evident approach is to have multiple servers. Efficiency of a replicated web server system will depend on the way of distributed incoming requests among these replicas. A distributed Webserver architectures schedule client requests among the multiple server nodes in a usertransparent way that affects the scalability and availability. The aim of this paper is the development of a load balancing techniques on distributed Web-server systems.

Dispatcher Based Dynamic Load Balancing on Web Server System

The traffic increasing in the network creates bulk congestion while the bulk transfer of data evolves. Performance evaluation and high availability of servers are important factors to resolve this problem using various cluster based systems. There are several low-cost servers using the load sharing cluster system which are connected to high speed networks, and apply load balancing technique between servers. It offers high computing power and high availability. A distributed website server can provide scalability and flexibility to manage with emergent client demands. Efficiency of a replicated web server system will depend on the way of distributed incoming requests among these replicas. A distributed Web-server architectures schedule client requests among the multiple server nodes in a user-transparent way that affects the scalability and availability. The aim of this paper is the development of a load balancing techniques on distributed Web-server systems.

Content distributing algorithm for replicated Web servers based on market models

AbstractA content distributing algorithm based on market models for a replication distribution scheme of Web contents is proposed. In general, replication distribution is considered to effectively utilize the time and space local properties of access from a client and has been the topic of numerous studies. However, maintaining QoS (such as shortening the content obtaining time) in replicated servers when servers are in a congested state has not been considered in these studies. Since replicated servers constitute a resource shared by multiple ISPs (Internet Service Providers), the accesses need to be limited to replicated servers in case of a congested state to maintain the QoS enjoyed by each client. Thus, in this paper, a scheme for determining allocation of access to replicated servers for each content during congestion based on market models is proposed. The analytical and simulation results have confirmed that the proposed method controls the QoS in accordance with the access arrival rate to each content. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(11): 9–19, 2001

Optimal Placement of Web Proxies for Replicated Web Servers in the Internet

Optimal Placement of Web Proxies for Replicated Web Servers in the Internet

QoS-based Architectures for Geographically Replicated Web Servers

In this paper, we discuss strategies for providing World Wide Web service users with adequate Quality of Service (i>QoS). We argue that QoS can be provided by distributing the service requests processing load among replicated Web servers (i>WSs), that can be geographically distributed across the Internet. In order to support our argument, we compare and contrast several load distribution strategies, and assess their effectivness when deployed within the context of a geographically replicated Web service; the principal figure of merit we use in this assessment is the response time experienced by the users of that service. As a result of this comparison, we propose a specific strategy, named i>QoS-based, that implements load distribution among WS replicas by binding a user to the replica that provides the shortest user response time. We examine several architectures that exploit our QoS-based strategy. Two of these architectures, named, respectively, i>Browser-based and i>Load Distribution-i>based, are described in detail as they are particularly appropriate for implementing our strategy.

Load distribution among replicated Web servers

A dominant factor for the success of an Internet based Web service is the Quality of Service (QoS) perceived by its users. The principal QoS attributes these users perceive include those related to the service "responsiveness", i.e. the service availability and timeliness. In this paper, we argue that QoS can be provided by distributing the processing load among replicated Web servers, and that these servers can be geographically distributed across the Internet. In this context, we discuss strategies for load distribution, and summarize a number of alternative architectures that can implement those strategies. The principal figure of merit we use in order to assess the effectiveness of the load distribution strategies we discuss is the response time experienced by the users.

A market-based architecture for management of geographically dispersed, replicated Web servers

Distributed Web sites require allocation mechanisms to dispatch request in a scalable and controllable manner among a set of replicated servers. Unlike most existing approaches, we propose a technique that pushes the allocation functionality onto the client and argue that this approach scales well and may result in increased performance in many cases. Building on theoretical work based on game theory, we show that the usage of individual replicas can be effectively controlled with cost functions even when the clients are noncooperative. We present the design and implementation of WebSeAl, our prototype system realizing these techniques, and present experiment results.

Application-layer anycasting: a server selection architecture and use in a replicated Web service

Server replication improves the ability of a service to handle a large number of clients. One of the important factors in the efficient utilization of replicated servers is the ability to direct client requests to the "best" server, according to some optimality criteria. In the anycasting communication paradigm, a sender communicates with a receiver chosen from an anycast group of equivalent receivers. As such, anycasting is well suited to the problem of directing clients to replicated servers. This paper examines the definition and support of the anycasting paradigm at the application-layer, providing a service that uses an anycast resolver to map an anycast domain name and a selection criteria into an IP address. By realizing anycasting in the application-layer, we achieve flexibility in the optimization criteria and ease the deployment of the service. As a case study, we examine the performance of our system for a key service: replicated Web servers. To this end, we develop an approach for estimating the response time that a client will experience when accessing given servers. Such information is maintained in the anycast resolver that clients query to obtain the identity of the server with the best estimated response time. Our performance collection technique combines server push with resolver probes to estimate the expected response time without undue overhead. Our experiments show that selecting a server using our architecture and estimation technique can improve the client response time by a factor of two over nearest server selection and by a factor of four over random server selection.

Selection algorithms for replicated Web servers

Replication of documents on geographically distributed servers can improve both performance and reliability of the Web service. Server selection algorithms allow Web clients to select one of the replicated servers which is "close" to them and thereby minimize the response time of the Web service. Using client proxy server traces, we compare the effectiveness of several "proximity" metrics including the number of hops between the client and server, the ping round trip time and the HTTP request latency. Based on this analysis, we design two new algorithms for selection of replicated servers and compare their performance against other existing algorithms. We show that the new server selection algorithms improve the performance of other existing algorithms on the average by 55%. In addition, the new algorithms improve the performance of the existing non-replicated Web servers on average by 69%.