ACDN

Abstract

Content delivery networks (CDNs) currently deliver mostly static and streaming content. However, proxy caches can improve the delivery of these content types as well. A unique value of CDNs could be in improving access to dynamic content, which cannot be cached by proxies. We refer to such a CDN as an Applications CDN, or ACDN. An ACDN will allow a content provider not to worry about the amount of resources provisioned for its application. Instead, it can deploy the application on a single computer anywhere in the network, and then the ACDN will replicate and migrate the application as needed by the observed demand. This demo shows a functional prototype of an ACDN. An ACDN has a fundamental difference with a traditional CDN oriented towards static content. A traditional CDN server is willing to satisfy any request for any content from the subscriber Web site, either from its cache or by obtaining the response from the origin server. In contrast, an ACDN server must have the requested application, including executables, underlying data, and the computing environment, to be able to process a request. Deploying an application at the time of the request is impractical; thus the ACDN can distribute requests only among the servers that currently have a replica of the application; at the same time, the applications must be placed on ACDN servers asynchronously with requests. Thus, ACDN must provide solutions for the following problems that traditional CDNs do not face: Application distribution framework: An ACDN needs a mechanism to deploy an application replica dynamically, and to keep the replica consistent. The latter issue is complicated by the fact that an application typically contains multiple components whose versions must be mutually consistent for the application to function properly. Content placement algorithm: An ACDN must decide which applications to deploy where and when. Content placement is solved trivially in traditional CDNs by cache replacement algorithms. Request distribution algorithm: in addition to load and proximity factors that traditional CDNs must consider, the request distribution mechanism in an ACDN must be aware of where in the system applications are currently deployed. An ACDN is different from Edge-Side Includes (ESI) from Akamai, 1 which divides a dynamic page into a static template and dynamic fragments and reconstructs the final page at cache servers. Unlike ACDNs, ESI cannot replicate com-