CDN
A globally distributed network of servers (edge servers) that cache and deliver content such as images, videos and web pages close to the user.
A CDN (Content Delivery Network) is the backbone of the modern internet. Over 50% of all internet traffic is delivered via CDNs – from streaming and e-commerce to corporate sites. By caching content on servers around the world and serving it from the nearest location, a CDN drastically reduces load times, offloads the origin server and helps protect against DDoS. Favourite providers include Cloudflare, AWS CloudFront, Akamai, Fastly and Vercel Edge Network.
What is CDN?
A Content Delivery Network (CDN) is a geographically distributed network of edge servers that cache copies of web content (images, CSS, JavaScript, videos, APIs) and deliver them to users from the nearest location. Instead of every request hitting a single origin data centre, the nearest CDN edge server answers – with much lower latency. Modern CDNs offer more than caching: edge computing, Web Application Firewall (WAF), DDoS protection, image optimization and even serverless functions.
How does CDN work?
When a user in Munich requests a page whose origin is in the US, DNS resolves the domain to the nearest CDN edge (e.g. Frankfurt). If the content is cached there (cache hit), it is served immediately – latency in the low milliseconds instead of 100+ ms. On a cache miss the edge fetches from the origin, stores the response locally and delivers it to the user. Future requests from the same or nearby locations are served from cache. Cache rules (TTL, Cache-Control headers) control how long content is cached.
Practical Examples
Netflix uses its own CDN (Open Connect) at 1,000+ locations worldwide – over 90% of traffic is served from local edge servers.
A German online shop uses Cloudflare CDN to serve product images worldwide in under 50 ms and increases conversion by 15%.
A news site distributes breaking stories via a CDN and handles traffic spikes of millions of readers without overloading the origin.
A SaaS company uses Vercel Edge Functions to personalize API responses at the edge with sub-25 ms latency globally.
A gaming platform distributes multi-GB game updates via a CDN to millions of players without straining its own infrastructure.
Typical Use Cases
Website performance: Deliver static assets (images, CSS, JS) worldwide with minimal latency
Video streaming: Serve films and live streams from distributed servers without buffering
E-commerce: Speed up product images and catalog pages globally for better conversion
DDoS protection: CDN as a shield that absorbs attack traffic across the global network
API acceleration: Cache or personalize API responses at the edge
Advantages and Disadvantages
Advantages
- Much lower load times: Content is served from the geographically nearest server
- High availability: If one edge fails, another takes over – global redundancy
- DDoS protection: The distributed CDN absorbs attack traffic before it reaches the origin
- Scalability: Traffic spikes are absorbed by the CDN without scaling the origin
- SEO benefit: Faster load times are a ranking factor for Google
Disadvantages
- Cost at high traffic: CDN fees are often based on data transfer and can be significant for video
- Cache invalidation: Updated content must be purged on all edge servers
- Complexity for dynamic content: Personalized or user-specific content is harder to cache
- Provider dependency: A global CDN outage affects all connected sites
Frequently Asked Questions about CDN
Do I need a CDN for my website?
What is the difference between CDN and caching?
How does a CDN affect SEO?
Related Terms
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