Content Delivery Network (CDN)

A CDN is a geographically distributed network of servers that caches and delivers content from locations close to end users, reducing latency and improving load times.

CDNs work by caching static assets (images, CSS, JavaScript, videos) at edge servers located in data centers around the world. When a user requests content, it is served from the nearest edge location rather than the origin server.

Beyond static content, modern CDNs also handle dynamic content acceleration, DDoS protection, TLS termination, and edge computing. Some CDNs support edge functions that run custom logic at the point of presence closest to the user.

In system design interviews, CDNs are essential for any system serving global users. Key considerations include cache invalidation strategies (TTL-based, purge APIs), cache hit ratios, and how to handle personalized or frequently changing content.

Popular CDN providers include Cloudflare, AWS CloudFront, Fastly, and Akamai.

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