Content Delivery Networks: Speeding Up the Web

A content delivery network (CDN) is a group of servers distributed around the world. When a user asks for a page or an asset, the CDN serves it from a nearby edge server instead of the origin. This shortens the travel distance and reduces delay, which makes sites feel faster.

How CDNs work

CDNs place many servers in different regions. When a user requests a file, the CDN routes the request to the closest edge location. Static assets like images, CSS, and JavaScript are cached at the edge, so repeated visits load quickly. If the content isn’t in cache or has expired, the edge fetches it from the origin.

  • Cache static assets at edge servers to cut travel time.
  • Control freshness with TTLs and HTTP headers such as Cache-Control.
  • Handle dynamic content by on‑demand fetches or edge computing features.
  • Use additional optimizations like image scaling, modern codecs, and HTTP/2 or HTTP/3.

Edge servers also offer security benefits. They can terminate TLS near the user, provide DDoS protection, and block malicious traffic before it reaches the origin.

Benefits and use cases

A CDN reduces latency, lowers the risk of outages, and helps handle traffic spikes. It improves user experience for global audiences, speeds media delivery, and supports software updates or large downloads without stressing a single data center. For sites with visitors from many regions, a CDN often pays for itself through faster load times and higher availability.

Choosing a CDN

  • Check coverage in target regions and typical latency to your users.
  • Look at performance metrics like time to first byte (TTFB) and cache hit rate.
  • Evaluate features: HTTP/2 or HTTP/3, TLS management, image optimization, edge functions, and easy content purging.
  • Consider pricing, support, and how the CDN integrates with your hosting.

Best practices

  • Set clear caching rules with Cache-Control and ETag headers.
  • Use asset versioning to bust caches when needed.
  • Enable rapid purges and, when possible, stale-while-revalidate.
  • Test performance with real user traffic and monitor results over time.

Edge features to consider

  • Edge computing for small, fast responses at the edge.
  • Image and video optimization at the edge for reduced file sizes.
  • Origin shield to protect the origin from bursty demand.

Examples

  • Many large providers offer global networks, but choosing a CDN often depends on regional needs, pricing, and ease of integration with existing systems.

Key Takeaways

  • A CDN brings content closer to users to reduce latency and improve reliability.
  • Caching rules and modern protocols maximize edge performance.
  • Evaluate coverage, performance, and edge features when choosing a CDN.