The general concept.
THE IDEA
Copies of your static files held at many locations around the world. A visitor receives them from a nearby location rather than from the origin server.
WHAT IT IMPROVES
Delivery time for visitors far from the server Bandwidth from the origin Resilience under load
WHAT IT DOES NOT IMPROVE
Page generation, unless HTML is cached A slow application Large unoptimised files, which are still large
HOW FILES GET THERE
On first request from a location, the CDN fetches from the origin and keeps a copy.
Subsequent requests from nearby are served locally.
THE CACHE HIT RATIO
The proportion served from the cache rather than fetched from the origin. Higher is better.
A low ratio means the CDN is adding a hop without much benefit.
WHEN A CDN MATTERS MOST
An international audience Media-heavy sites Traffic spikes
WHEN IT MATTERS LEAST
A small site with local visitors, already cached and optimised.
Honest assessment matters here; a CDN is not automatically an improvement.
