Replication for Web Hosting Systems

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. Th

Latency-driven replication for globally distributed systems

Steen, M.R. van [Promotor]Pierre, G.E.O. [Copromotor

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

Content Replication in Web++

Web++ is a prototype system that supports user transparent wide area replication of resources in order to improve the response time and reliability of the HTTP service. Our architecture is based on smart clients, and can be dynamically downloaded as mobile code into a user's application, presents a number of advantages. Clients keep track of the average HTTP latency that they experience from various servers and use that information in order to make to choose the replica of a resource that is expected to deliver the best response time for them. The clients also provide feedback on the observed request latencies to the servers, which allows helps the servers to determine which resources should be replicated and what would be the best locations for the replicas. We describe in this paper a distributed server-initiated approach for resource replication in which all servers can decide autonomously whether to replicate resources and the locations where the replicas should be allocated. In addition to the novel use of smart clients, our algorithm also avoids keeping track of complex network topologies by using the concept of logical segments. We present the results of experiments that show that our algorithm for resource allocation scale well with respect to the number of servers and the number of replicated resources