Keyboard shortcuts

Press ← or → to navigate between chapters

Press S or / to search in the book

Press ? to show this help

Press Esc to hide this help

CDNs

Content Delivery Networks (CDNs) cache content at edge locations worldwide, reducing latency by serving users from nearby servers.

How CDNs Work

┌─────────────────────────────────────────────────────────────────────┐
│                      CDN Architecture                               │
├─────────────────────────────────────────────────────────────────────┤
│                                                                     │
│           Origin Server (Your Server)                               │
│                    │                                                │
│        ┌──────────┼──────────┐                                      │
│        │          │          │                                      │
│        ▼          ▼          ▼                                      │
│   ┌────────┐ ┌────────┐ ┌────────┐                                  │
│   │  Edge  │ │  Edge  │ │  Edge  │                                  │
│   │  US    │ │  EU    │ │  Asia  │                                  │
│   └────┬───┘ └────┬───┘ └────┬───┘                                  │
│        │          │          │                                      │
│        ▼          ▼          ▼                                      │
│      Users      Users      Users                                    │
│                                                                     │
│   User requests → Nearest Edge → Cached response (fast!)            │
│   Cache miss → Edge fetches from Origin → Caches → Responds         │
│                                                                     │
└─────────────────────────────────────────────────────────────────────┘

Benefits

Performance:
  - Reduced latency (content closer to users)
  - Faster page loads
  - Better user experience

Scalability:
  - Offload traffic from origin
  - Handle traffic spikes
  - Global reach without global infrastructure

Availability:
  - DDoS protection
  - Origin failover
  - Always-on edge presence

What to Put on CDN

Ideal for CDN:
  ✓ Static files (JS, CSS, images)
  ✓ Videos and media
  ✓ Downloadable files
  ✓ Public API responses (if cacheable)

Not for CDN (usually):
  ✗ User-specific content
  ✗ Real-time data
  ✗ Authenticated endpoints
  ✗ Frequently changing data

Cache Control

# Cache for 1 day, revalidate after
Cache-Control: public, max-age=86400, must-revalidate

# Cache for 1 year (immutable assets)
Cache-Control: public, max-age=31536000, immutable

# No caching
Cache-Control: no-store

# Private only (not CDN)
Cache-Control: private, max-age=3600

CDN Configuration Concepts

TTL (Time To Live):
  How long edge caches content
  Balance freshness vs. origin load

Cache Keys:
  What makes requests "same" for caching
  URL, headers, cookies, query strings

Purge/Invalidation:
  Force refresh of cached content
  By URL, tag, or entire cache

Edge Functions:
  Run code at edge (Cloudflare Workers, Lambda@Edge)
  Customize responses, A/B testing, auth

Global CDNs:
  - Cloudflare: Free tier, security focus
  - Fastly: Real-time purging, edge compute
  - Akamai: Enterprise, largest network
  - AWS CloudFront: AWS integration
  - Google Cloud CDN: GCP integration

Specialized:
  - Bunny CDN: Cost-effective
  - KeyCDN: Simple pricing
  - imgix: Image optimization focus

Setting Up CDN

Basic setup:
  1. Sign up with CDN provider
  2. Configure origin (your server)
  3. Get CDN domain (e.g., cdn.example.com)
  4. Update DNS or reference CDN URLs
  5. Configure cache rules

DNS example:
  cdn.example.com CNAME example.cdn-provider.net

Or full site through CDN:
  example.com → CDN → origin.example.com

Debugging CDN

# Check cache status
$ curl -I https://cdn.example.com/image.png
X-Cache: HIT          # Served from edge
X-Cache: MISS         # Fetched from origin
CF-Cache-Status: HIT  # Cloudflare specific

# Check which edge served request
$ curl -I https://cdn.example.com/image.png
CF-RAY: 123abc-SJC    # Cloudflare San Jose

# Bypass cache
$ curl -H "Cache-Control: no-cache" https://cdn.example.com/image.png