What is a CDN? A Clear Guide

A CDN caches content at edge locations worldwide to reduce latency and speed up delivery. Learn how CDNs work, key concepts, and when your team needs one.

The EaseCloud Team

18 Aug 2026 • 2 min read

A Content Delivery Network (CDN) is a globally distributed network of servers that caches and delivers content from locations physically close to end users. CDNs reduce latency, accelerate page load times, and offload traffic from origin servers by serving cached copies of static and dynamic content from edge locations around the world.

Why CDNs Matter

Page load speed directly impacts user engagement and revenue. Google research shows that a 1-second delay in mobile page load time can reduce conversions by up to 20%. CDNs address this by serving content from the nearest edge location rather than routing every request to a distant origin server. For European businesses serving global users, a CDN can reduce page load times from 2-3 seconds to under 500 milliseconds for static assets. CDNs also absorb traffic spikes and mitigate DDoS attacks by distributing load across hundreds of edge nodes instead of concentrating it on a single origin.

How CDNs Work

When a user requests a webpage or asset, the CDN routes that request to the nearest edge server rather than the origin:

DNS routing: When a user requests content, DNS resolves to the CDN's nearest point of presence (PoP) based on geographic proximity or network latency.
Cache check: The edge server checks if it has a fresh cached copy of the requested content. If yes, it serves the content immediately without contacting the origin.
Origin fetch: If the content is not cached or has expired, the edge server retrieves it from the origin server, delivers it to the user, and stores a copy for subsequent requests.
Cache invalidation: When content changes, the origin instructs the CDN to purge stale copies. This happens through TTL (time-to-live) expiration or explicit purge commands.

Modern CDNs also support edge compute, allowing logic to run at edge locations for tasks like A/B testing, geo-based redirects, and request authentication without round-trips to the origin.

Key Concepts

Edge location (Point of Presence): A data center in the CDN's network positioned close to end users. Major CDNs operate 200-400+ PoPs across six continents.
Cache hit ratio: The percentage of requests served from cache versus fetched from the origin. A well-configured CDN achieves 90%+ cache hit ratios for static content.
Time-to-live (TTL): The duration a cached object remains valid before the edge server must revalidate or fetch a fresh copy from the origin. Shorter TTLs ensure fresher content; longer TTLs reduce origin load.
Origin shield: An intermediate cache layer between edge servers and the origin that reduces the number of requests hitting your origin server, especially useful during cache misses across many edge locations.
Anycast routing: A networking technique where multiple servers share the same IP address and traffic is routed to the nearest one. Most CDNs use anycast to direct users to the closest edge location automatically.

When You Need a CDN

Your users are geographically distributed and users far from your origin server experience slow load times. A European origin serving users in Asia or the Americas benefits immediately from edge caching.
You serve large volumes of static assets - images, CSS, JavaScript, videos, software downloads - and your origin server is struggling under the load or bandwidth costs are rising.
Your application experiences traffic spikes during product launches, marketing campaigns, or seasonal peaks, and your origin infrastructure cannot absorb the burst without degradation.
You need DDoS protection and want to absorb volumetric attacks at the network edge before they reach your origin infrastructure.
GDPR and data residency matter to your business and you need to control which edge locations cache user-specific data versus which serve only static, non-personal assets.