Distributed delivery
A content delivery network distributes content across multiple locations. Suitable files can be cached and served from an appropriate edge server, potentially reducing load times and origin load. The selected location is not necessarily the geographically closest one; routing and load also matter.
Cache hits and misses
A cache hit means a reusable response is available. On a miss, the CDN may need to fetch it from the origin. Cache-Control, expiry times, cache keys and invalidation determine reuse. Personalized or sensitive responses must not accidentally be cached for other visitors.
DNS, anycast and security
CDNs may use DNS-based selection or anycast. With anycast, the same address is announced from multiple locations. DNS can therefore return CDN addresses rather than origin addresses. This alone does not prevent direct access to the origin. TLS, firewall rules and any DDoS or WAF features need suitable configuration.
What do our tests show?
DNS, TLS and HTTP tests run from our server in Düsseldorf. They may reach a different CDN endpoint than a visitor in another country. A good result at this location does not guarantee identical worldwide load times. When troubleshooting, examine cache, CDN and origin separately and use the actual hostname.