Walrus-a low latency, high throughput Web service using Internet-wide replication (original) (raw)
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Seamlessly selecting the best copy from internet-wide replicated web servers
Lecture Notes in Computer Science, 1998
The explosion of the web has led to a situation where a majority of the traffic on the Internet is web related. Today, practically all of the popular web sites are served from single locations. This necessitates frequent long distance network transfers of data (potentially repeatedly) which results in a high response time for users, and is wasteful of the available network bandwidth. Moreover, it commonly creates a single point of failure between the web site and its Internet provider. This paper presents a new approach to web replication, where each of the replicas resides in a different part of the network, and the browser is automatically and transparently directed to the "best" server. Implementing this architecture for popular web sites will result in a better response-time and a higher availability of these sites. Equally important, this architecture will potentially cut down a significant fraction of the traffic on the Internet, freeing bandwidth for other uses.
QoS-based architectures for geographically replicated Web servers
Cluster Computing, 2001
In this paper, we discuss strategies for providing World Wide Web service users with adequate Quality of Service (QoS). We argue that QoS can be provided by distributing the service requests processing load among replicated Web servers (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 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, Browser-based and Load Distribution-based, are described in detail as they are particularly appropriate for implementing our strategy.
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.
Towards On-Demand Web Application Replication
2003
The increasing popularity of Web applications drives the need for systems that offer improve high performance web services by replicating applications at geographically distributed servers. In this paper, we propose a system for Web application replication that replicates both application code and its data. A key challenge in such a system is data replication and consistency, so that each replica server can access its shared data locally thereby avoiding the widearea network latency that would be incurred by a traditional ...
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).
High Reliability Replication Technique for Web-Server Cluster Systems
International Conference on Computational Science, 2005
Providing reliable and efficient services are primary goals in designing a web server system. Data replication can be used to improve the reliability of the system. However, mapping mechanism is one of the primary concerns to data replication. In this paper, we propose a mapping mechanism model called enhanced domain name server (E-DNS) that dispatches the user requests through the
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.
Document replication and distribution in extensible geographically distributed web servers
Journal of Parallel and Distributed Computing, 2003
A geographically distributed web server (GDWS) system, consisting of multiple server nodes interconnected by a MAN or a WAN, can achieve better efficiency in handling the ever-increasing web requests than centralized web servers because of the proximity of server nodes to clients. It is also more scalable since the throughput will not be limited by available bandwidth connecting to a central server. The key research issue in the design of GDWS is how to replicate and distribute the documents of a website among the server nodes. This paper proposes a density-based replication scheme and applies it to our proposed Extensible GDWS (EGDWS) architecture. Its document distribution scheme supports partial replication targeting only at hot objects among the documents. To distribute the replicas generated via the density-based replication scheme, we propose four different document distribution algorithms: Greedy-cost, Maximal-density, Greedypenalty, and Proximity-aware. A proximity-based routing mechanism is designed to incorporate these algorithms for achieving better web server performance in a WAN environment. Simulation results show that our document replication and distribution algorithms achieve better response times and load balancing than existing dynamic schemes. To further reduce user's response time, we propose two document grouping algorithms that can cut down on the request redirection overheads.
Efficient and scalable replication of services over wide-area networks
2013
Service replication ensures reliability and availability, but accomplishing it requires solving the total-order problem of guaranteeing that all replicas receive service requests in the same order. The problem, however, cannot be solved for a specific combination of three factors, namely, when (i) the message transmission delays cannot be reliably bounded, as often the case over wide-area networks such as the Internet, (ii) replicas can fail, e.g., by crashing, the very events that have to be tolerated through replication, and finally (iii) the solution has to be deterministic as distributed algorithms generally are. Therefore, total-order protocols are developed by avoiding one or more of these three factors by resorting to realistic assumptions based on system contexts. Nevertheless, they tend to be complex in structure and impose time overhead with potentials to slow down the performance of replicated services themselves. This thesis work develops an efficient total-order protocol by leveraging the emergence of cluster computing. It assumes that a server replica is not a stand-alone computer but is a part of a cluster from which it can enlist the cooperation of some of its peers for solving the total-order problem locally. The local solution is then globalised with replicas spread over a wide-area network. This two-staged solution is highly scalable and is experimentally demonstrated to have a smaller performance overhead than a single-stage solution applied directly over a wide-area network. The local solution is derived from an existing, multi-coordinator protocol, Mencius, which is known to have the best performance. Through a careful analysis, the derivation modifies some aspects of Mencius for further performance improvements while retaining the best aspects.
Proceedings of the 2005 ACM symposium on Applied computing - SAC '05, 2005
Efficient server selection algorithms reduce retrieval time for objects replicated on different servers and are an important component of Internet cache architectures. This paper empirically evaluates six clientside server selection algorithms. The study compares two statistical algorithms, one using median bandwidth and the other median latency, a dynamic probe algorithm, two hybrid algorithms, and random selection. The server pool includes a topologically dispersed set of United States state government web servers. Experiments were run on three clients in different cities and on different regional networks. The study examines the effects of time-of-day, client resources, and server proximity. Differences in performance highlight the degree of algorithm adaptability and the effect that network upgrades can have on statistical estimators. Dynamic network probing performs as well or better than the statistical bandwidth algorithm and the two probe-bandwidth hybrid algorithms. The statistical latency algorithm is clearly worse, but does outperform random selection.