| Shared application-level Web infrastructures such as Content Distribution Networks (CDNs) and computing utility platforms (e.g., Amazon EC2) have become an essential part of the Internet. As these platforms mature, it is becoming plausible for them to converge to a comprehensive form of service whereby the service provider is responsible for supplying businesses with all their infrastructure needs in a scalable, efficient, and transparent manner.;This dissertation addresses three problems toward realizing this type of comprehensive platforms. The first problem is the high cost and long delay of enacting Web application (re-)placement decisions which constrains application placement algorithms in terms of the rate at which placement decisions could be revisited. In this regard, we propose, implement, and evaluate various mechanisms to significantly reduce the amount of time and resources needed to enact application placements. In the second problem we address the issue of connection disruptions in hosting platforms that use IP anycast mechanisms to route end-users' requests to hosting servers. Connections can be disrupted in these platforms because IP routes can change in the middle of a download which can cause packets from a connection to arrive at a different server, which would reset the connection and thus disrupt the download. To this end, we propose a simple and efficient mechanism to handle connection disruptions in these platforms. Lastly, we study the issue of Web timeouts in a Web hosting platform. We find that there is a big mismatch between the timeouts exhibited in today's Web servers and the actual time Web clients take to perform various activities. This opens the door for the so-called claim-and-hold DoS attacks, where an attacker claims server resources and holds them as long as possible while spending minimal amount of resources of its own. We propose to significantly reduce timeouts when the server becomes low on resources, and we demonstrate how this can protect servers against these attacks. |
