CDN and Edge Logic

1. A Cache Hierarchy You Rent

A content delivery network is a cache, and almost everything in this module still applies to it. What changes is ownership, and three consequences follow from that.

• You do not control eviction. An entry can disappear long before its expiry because the location serving your users needed the space for somebody else's traffic. Hit rate is therefore a measurement rather than a calculation.
• There are hundreds of independent copies. Each location caches separately, so one object can be missing in one city and present in the next.