cdn-architecture

# CDN Architecture

Comprehensive guide to Content Delivery Network architecture - caching, distribution, and edge optimization patterns.

## When to Use This Skill

- Designing CDN strategies for web applications
- Implementing cache hierarchies
- Optimizing origin load and performance
- Understanding cache invalidation patterns
- Selecting CDN providers and features
- Configuring edge caching rules

## CDN Fundamentals

### How CDNs Work

```text
Without CDN:
User (Tokyo) ───────────────────► Origin (New York)
              2000km, ~200ms RTT

With CDN:
User (Tokyo) ──► Edge (Tokyo) ──► Origin (New York)
              <10km, ~10ms RTT    (only on cache miss)

CDN Benefits:
├── Reduced latency (content served from nearby)
├── Origin offload (fewer requests hit origin)
├── DDoS protection (distributed, absorbs attacks)
├── Scalability (handles traffic spikes)
└── Reliability (multiple POPs for redundancy)
```

### CDN Architecture

```text
CDN Components:

┌─────────────────────────────────────────────────────────┐
│                     Internet                             │
└────────────────────────┬────────────────────────────────┘
                         │
         ┌───────────────┼───────────────┐
         │               │               │
    ┌────▼────┐    ┌────▼────┐    ┌────▼────┐
    │  Edge   │    │  Edge   │    │  Edge   │
    │ POP 1   │    │ POP 2   │    │ POP 3   │
    │(Tokyo)  │    │(London) │    │(NY)     │
    └────┬────┘    └────┬────┘    └────┬────┘
         │               │               │
         └───────────────┼───────────────┘
                         │
              ┌──────────▼──────────┐
              │    Origin Shield    │
              │    (Mid-tier)       │
              └──────────┬──────────┘
                         │
              ┌──────────▼──────────┐
              │       Origin        │
              │    (Your servers)   │
              └─────────────────────┘

Terminology:
- POP: Point of Presence (edge location)
- Edge