Why does YouTube load so quickly no matter where you are in the world? How can Netflix stream 4K video to millions of users simultaneously? The answer: Content Delivery Networks (CDNs).
CDNs are distributed networks of servers that cache and deliver content from locations close to users. They’re essential for any service that serves static content (images, videos, CSS, JavaScript) to a global audience.
What You’ll Learn
In this section, we’ll explore:
- What is a CDN?: Understanding the basic architecture and purpose
- How CDNs work: Request routing, caching, and origin servers
- Cache invalidation: Keeping content fresh and handling updates
- CDN strategies: Push vs pull, cache eviction policies
- Geographic distribution: Edge servers and points of presence (PoPs)
- Performance optimisations: Compression, image optimisation, HTTP/2
- Security: DDoS protection and SSL/TLS at the edge
Why CDNs Matter
CDNs solve critical problems for modern web applications:
- Reduced latency: Serve content from servers close to users
- Bandwidth savings: Reduce load on your origin servers
- Improved availability: Content remains available even if origin servers fail
- Better user experience: Faster page loads mean happier users
- Global scale: Serve users worldwide without building data centres everywhere
In system design interviews, CDNs are often the answer to “How would you serve content to users globally?”
Real-World Usage
Almost every major website uses a CDN:
- YouTube and Netflix use CDNs to stream video efficiently
- Facebook and Instagram serve images from CDN edge servers
- E-commerce sites use CDNs to ensure fast page loads during sales
- News websites handle traffic spikes with CDN caching
Understanding CDNs is crucial for designing any content-heavy or global application. Let’s dive in!