High Reliability Replication Technique for Web-Server Cluster Systems (original) (raw)
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Implementing highly-available www servers based on passive object replication
1999
Abstract We investigate issues related to building highly available World Wide Web (WWW) servers on workstation clusters. We present a novel architecture that includes a dynamic Domain Name System (DNS) and a WWW server based on passive object replication. This architecture allows us to reduce the service down-time of a WWW server without impacting on the Hyper Text Transfer Protocol (HTTP) protocol (and thus on the WWW client software).
As more and more organizations rely on using multiple low-end servers to carry out the Web service function, a major challenge of how to arrange these low-end servers to achieve goals such as availability and scalability. As both replication and clustering have their shortcomings; an integration approach is needed. Such approach has to consider also security requirements as it interferes in the arrangements too. This paper describes a new architecture that integrates clustering and replication with necessary security. We present an example implementation of such architecture in Microsoft Windows environment. We conducted an experimental study to examine the architecture and found that it presented the desired performance improvement while maintain the utilization to an acceptable level.
Replication algorithms for the World-Wide Web
Journal of Systems Architecture, 2004
This paper addresses the two fundamental issues in replication, namely deciding on the number and placement of the replicas and the distribution of requests among replicas. We first introduce a static centralized algorithm for replicating objects that can keep a balanced load on servers. To better meet the requirements of the dynamic nature of the Internet traffic and the rapid change in the access pattern of the WWW, we also propose a dynamic distributed algorithm where each server relies on some collected information to decide on where to replicate and migrate objects to achieve good performance and faulttolerance levels.
Walrus-a low latency, high throughput Web service using Internet-wide replication
International Conference on Distributed Computing Systems Workshops, 1999
Today, most of the popular web sites are served from single locations. This basic Web client-server model is easy to deploy and maintain and thus is very successful. It suffers, however, from several efficiency and availability problems. This paper presents Walrus, a low-latency, high-throughput Web service that addresses some of these problems. Under Walrus, a single logical Web server can be replicated to several clusters of identical servers where each cluster resides in a different part of the Internet. An important aspect of Walrus is its ability to transparently direct the web browser to the best replica without any changes to the web server, web client, and network infrastructure. "Best" is a relative term, dependent on where the client is located on the network, the load on each replica, and more. Walrus deploys an elegant algorithm that balances these considerations.
Replication for Web Hosting Systems
ACM Computing …, 2004
Replication is a well-known technique to improve the accessibility of Web sites. It generally offers reduced client latencies and increases a site's availability. However, applying replication techniques is not trivial, and various Content Delivery Networks (CDNs) have been created to facilitate replication for digital content providers. The success of these CDNs has triggered further research efforts into developing advanced Web replica hosting systems. These are systems that host the documents of a Web site and manage replication automatically. To identify the key issues in designing a wide-area replica hosting system, we present an architectural framework. The framework assists in characterizing different systems in a systematic manner. We categorize different research efforts and review their relative merits and demerits. As an important side-effect, this review and characterization shows that there a number of interesting research questions that have not received much attention yet, but which deserve exploration by the research community.
Reliable Partial Replication of Contents in Web Clusters: Getting Storage without losing Reliability
Journal of Computers, 2006
Traditionally, distributed Web servers have used two strategies for allocating files on server nodes: full replication and full distribution. While full replication provides a highly reliable solution, it limits storage capacity to the capacity of the smallest node. On the other hand, full distribution provides higher storage capacity at the cost of lower reliability. A hybrid solution is partial replication where every file is allocated to a small number of nodes. The most promising architecture for a partial replication strategy is the Web cluster architecture. However, Web clusters present a big flaw from reliability perspective as they contain a single point of failure. To correct this flaw, in this paper we present a modified architecture: the Web cluster with distributed Web switch. Reliability of Web clusters is evaluated for different replication strategies. System evaluations show that our proposal leads to a highly reliable solution with high scalability.
Redirection Algorithms for Load Sharing in Distributed Web-server Systems
1999
is necessary to support high request rates to popular Web sites. A clustered Web-server organization is preferable to multiple independent mirrored-servers because it maintains a single interface to the users and has the potential to be more scalable, fault-tolerant and better load balanced. In this paper we propose a Web cluster architecture in which the Domain Name System server (DNS), that dispatches the user requests among the servers through the URL-name to IP-address mapping mechanism, is integrated with a redirection request mechanism based on the HTTP protocol. This should alleviate the side effect of caching the IP-address mapping at intermediate name servers. We compare many alternative mechanisms, including synchronous vs asynchronous activation, and centralized vs distributed decision on redirection. Moreover, we analyze reassignment of entire domains or individual client requests, different types of status information, and different server selection policies for redirecting requests. Our results show that the combination of centralized and distributed dispatching policies allows the Web-server cluster to handle the high load skews in the WWW environment.
WS-replication: a framework for highly available web services
2006
Due to the rapid acceptance of web services and its fast spreading, a number of mission-critical systems will be deployed as web services in next years. The availability of those systems must be guaranteed in case of failures and network disconnections. An example of web services for which availability will be a crucial issue are those belonging to coordination web service infrastructure, such as web services for transactional coordination (e.g., WS-CAF and WS-Transaction). These services should remain available despite site and connectivity failures to enable business interactions on a 24x7 basis. Some of the common techniques for attaining availability consist in the use of a clustering approach. However, in an Internet setting a domain can get partitioned from the network due to a link overload or some other connectivity problems. The unavailability of a coordination service impacts the availability of all the partners in the business process. That is, coordination services are an example of critical components that need higher provisions for availability. In this paper, we address this problem by providing an infrastructure, WS-Replication, for WAN replication of web services. The infrastructure is based on a group communication web service, WS-Multicast, that respects the web service autonomy. The transport of WS-Multicast is based on SOAP and relies exclusively on web service technology for interaction across organizations. We have replicated WS-CAF using our WS-Replication framework and evaluated its performance.