A content delivery network is a distributed set of servers, often called edge locations or points of presence, that store copies of a site's files and serve them from the location nearest each visitor. CDNs reduce latency, absorb traffic spikes and protect the origin server from overload and attacks. Most modern hosting platforms include one by default.
How a CDN works
When a request arrives, the nearest edge checks its cache. If it has a fresh copy, it responds directly, which is a cache hit. If not, it fetches from your origin server, returns the response and stores a copy for the next visitor, according to the caching headers you set. Static assets like images, CSS and JavaScript are cached almost always; HTML can be cached too, with care.
SEO effects
Serving HTML from the edge can lower Time to First Byte for users and crawlers alike, which helps Largest Contentful Paint. CDNs also keep a site up under load, which avoids the 5xx errors that make Googlebot slow down. Many CDNs add features relevant to SEO, such as redirect rules, header editing and bot management.
- Lower latency and faster TTFB
- Fewer server errors during spikes
- Edge redirects and header rules without app deploys
- Bot management, which needs careful configuration for search crawlers
Things to watch
Bot protection features can block or challenge legitimate crawlers if they are set too aggressively. Cached HTML can serve stale pages after an update unless you purge or set short lifetimes. Geo-based behavior, such as redirecting visitors by country, can stop crawlers, which mostly crawl from US IP addresses, from seeing other regional versions.
Example
A bot rule that challenged crawlers
Driftcairn turns on a CDN bot-fight mode after a scraping incident. Within days, Search Console reports a rise in crawl errors, because Googlebot is being served a JavaScript challenge. The team switches to a rule that allows verified search engine crawlers and challenges only unverified bots.
Common mistakes
Blocking verified crawlers
Check that your CDN's bot settings allow known search and AI crawlers you want, verified by IP or reverse DNS.
Caching HTML without a purge plan
If HTML is cached at the edge, publishing must trigger a purge, or fixes will not appear for users or crawlers.
Questions
Not if it serves your content on your own domain. Duplicates arise only if the CDN exposes a second public hostname that serves the same pages.
