Measuring the impact of CDN design decisions

High performance Internet services are critical to the success of online businesses because poor user experience directly impacts revenue. To provide low latency and high availability service, companies often use content delivery networks CDNs to deliver content quickly and reliably to customers through a globally distributed network of servers. In order to meet the performance demands of customers, CDNs continuously make crucial network designs decisions that impact end-user performance. However, little is known about how CDN design decisions impact end-user performance or how to evaluate them effectively. ❧ In this thesis, we aim to help content providers and researchers understand the performance impact of CDN design changes on end-users. To achieve this, we examine a collection of measurement results and a Internet measurement system deployed in production at a large content provider. With our measurement results we will look at the impact of two important CDN design decisions—expansion of CDN front-end deployment and a choice of popular redirection strategies. Our design and evaluation of a measurement system at Microsoft demonstrates how CDNs can use end-user Internet measurements to support operations. ❧ First, we look at a massive expansion of Google's serving infrastructure into end-user networks to reduce latency to their services. We first explore measurement techniques using the client-subnet-prefix DNS extension to completely enumerate and geolocate Google's serving infrastructure. Our longitudinal measurements then capture a large expansion of Google sites from primarily on Google's own network into end-user networks, greatly reducing the distance between end-users and Google services. We then examine the performance impact of Google's expansion by conducting a study of user performance to the servers users are directed to before and after the expansion. ❧ Second, we examine Odin, a production measurement system deployed at Microsoft to support CDN and network operations. Odin was designed to overcome the measurement limitations of existing approaches and to take advantage of Microsoft's control of first-party end-user applications. We demonstrate that Odin delivers measurements even in the presence of Internet outages and supports a number of critical CDN operational scenarios such as traffic management, outage identification, and network experimentation. ❧ Third, we look at anycast and DNS redirection, the two common strategies used for serving latency sensitive content. We first examine a technique for constructing DNS latency maps that improves performance over existing approaches. We then use that approach to compare performance of DNS and anycast redirection where we find that most of the time anycast directs users to low latency server but DNS performance is better in the tail.