Too Long; Didn't Read
The CDN is just a massively distributed caching layer. There are 3 all-important metrics to measure: cold cache latency, hot cache latency and warm cache latency. Cold cache latency is much slower than the hot cache, but the warm cache is much more ambiguous as it must be fetched at some time away from the cold and hot cache tests. On CloudFront, for example, I’m seeing a drop from 1.2 seconds to 0.232 seconds in the cold cache test.