CDN
Acronymcontent-delivery-network, edge, edge networkDefinition
Content delivery network — a fleet of servers placed near readers that serve a site’s static files, and often its cached pages, from the nearest one, so that distance to the origin stops being the latency; the edge is also where TLS terminates, where bots are stopped, and where a DDoS is absorbed
Cloudflare is this site’s: DNS, the certificate, the edge cache and the firewall, in front of Railway’s origin in one region. A 304 from the edge never touches the origin; a 502 means the edge reached for the origin and found nothing there. What a CDN cannot do is cache a page that varies by viewer — which is why the navigation and the feed page send no-store, and why the feed XML, built for the anonymous viewer, can be cached an hour.
The part of the internet that makes a site in one data center feel local everywhere. Also the part that answers first when the origin is down, which is why an outage sometimes shows as a stale page rather than an error.