  Content delivery networks (CDN) contribute more than 50% of today's Internet
traffic. Meta-CDNs, an evolution of centrally controlled CDNs, promise
increased flexibility by multihoming content. So far, efforts to understand the
characteristics of Meta-CDNs focus mainly on third-party Meta-CDN services. A
common, but unexplored, use case for Meta-CDNs is to use the CDNs mapping
infrastructure to form self-operated Meta-CDNs integrating third-party CDNs.
These CDNs assist in the build-up phase of a CDN's infrastructure or mitigate
capacity shortages by offloading traffic. This paper investigates the Apple CDN
as a prominent example of self-operated Meta-CDNs. We describe the involved
CDNs, the request-mapping mechanism, and show the cache locations of the Apple
CDN using measurements of more than 800 RIPE Atlas probes worldwide. We further
measure its load-sharing behavior by observing a major iOS update in Sep. 2017,
a significant event potentially reaching up to an estimated 1 billion iOS
devices. Furthermore, by analyzing data from a European Eyeball ISP, we
quantify third-party traffic offloading effects and find third-party CDNs
increase their traffic by 438% while saturating seemingly unrelated links.
