Going Viral: Flash Crowds in an Open CDN Patrick Wendell* Michael J. Freedman U.C. Berkeley Princeton University Berkeley, CA, USA Princeton, NJ, USA
[email protected] [email protected] Abstract To insure themselves against the risk of a flash crowd, sites can outsource static content distribution to CDNs such as Akamai, which Handling flash crowds poses a difficult task for web services. Con- distribute traffic surges over a global network of content caches. This tent distribution networks (CDNs), hierarchical web caches, and strategy, however, does not generally address dynamically generated peer-to-peer networks have all been proposed as mechanisms for content, where CPU cycles are required to construct user-customized mitigating the effects of these sudden spikes in traffic to under- pages. To fill this gap, services are increasingly using cloud infras- provisioned origin sites. Other than a few anecdotal examples of tructure (such as Amazon EC2) to scale dynamic content creation isolated events to a single server, however, no large-scale analysis of in a similar fashion. Provisioning new resources in the cloud, while flash-crowd behavior has been published to date. not instantaneous, can be done orders-of-magnitude more quickly In this paper, we characterize and quantify the behavior of thou- than purchasing and installing new hardware. sands of flash crowds on CoralCDN, an open content distribution While flash crowds have long been used as anecdotal motivation network running at several hundred POPs. Our analysis considers for elastic-computing platforms, little research exists characteriz- over four years of CDN traffic, comprising more than 33 billion ing such events in an operational CDN.