A Content Delivery Network (CDN) is a geographically distributed network of servers that work together to deliver web content faster by serving it from locations closer to users. Instead of every user fetching content from one origin server, they get it from the nearest CDN server.
How CDNs Work
- You upload content to your origin server
- CDN copies it to servers worldwide ("edge servers" or "PoPs")
- User requests content
- CDN routes them to nearest server
- Content delivered from close proximity = faster
What CDNs Cache
Static Content
- Images
- CSS files
- JavaScript files
- Fonts
- Videos
- Downloads
Dynamic Content
Modern CDNs can also cache:
- API responses
- HTML pages
- Personalized content (with smart caching)
Benefits of CDNs
Speed
Content from a server 50ms away vs. 500ms away makes a noticeable difference.
Reliability
If one server goes down, others continue serving. Redundancy is built in.
Scalability
Handle traffic spikes without your origin server collapsing.
DDoS Protection
CDNs absorb malicious traffic before it reaches your server.
Bandwidth Savings
Cached content doesn't hit your server, reducing bandwidth costs.
Global Reach
Perform well for users worldwide, not just near your server.
Popular CDN Providers
General Purpose
- Cloudflare: Popular, generous free tier, security features
- Fastly: Real-time, developer-friendly
- Akamai: Enterprise, massive network
Cloud Provider CDNs
- CloudFront (AWS)
- Cloud CDN (Google Cloud)
- Azure CDN (Microsoft)
Specialized
- Imgix: Image optimization
- Mux: Video delivery
- Bunny CDN: Budget-friendly
CDN Configuration
Key decisions:
- Cache TTL: How long content stays cached
- Cache invalidation: How to update cached content
- Origin shields: Reduce load on origin server
- Edge computing: Run code at edge locations
When You Need a CDN
- Global audience
- Media-heavy site
- High traffic
- Performance is critical
- Security concerns
For small, local businesses? A CDN helps but isn't critical.