Footprint Descriptors: Theory and Practice of Cache Provisioning in a Global CDN

Modern CDNs cache and deliver a highly-diverse set of traffic classes, including web pages, images, videos and software downloads. It is economically advantageous for a CDN to cache and deliver all traffic classes using a shared distributed cache server infrastructure. However, such sharing of cache resources across multiple traffic classes poses significant cache provisioning challenges that are the focus of this paper. Managing a vast shared caching infrastructure requires careful modeling of user request sequences for each traffic class. Using extensive traces from Akamai's CDN, we show how each traffic class has drastically different object access patterns, object size distributions, and cache resource requirements. We introduce the notion of a footprint descriptor that is a succinct representation of the cache requirements of a request sequence. Leveraging novel connections to Fourier analysis, we develop a footprint descriptor calculus that allows us to predict the cache requirements when different traffic classes are added, subtracted and scaled to within a prediction error of 2.5%. We integrated our footprint calculus in the cache provisioning operations of the production CDN and show how it is used to solve key challenges in cache sizing, traffic mixing, and cache partitioning.