CDN (Content Delivery Network)

CDN Nədir?

CDN (Content Delivery Network) - content-i istifadəçilərə coğrafi olaraq yaxın server-lərdən çatdırmaq üçün istifadə olunan geografik bölgülərə yerləşdirilmiş server-lər şəbəkəsidir.

Məqsədlər:

Latency-nin azaldılması
Bandwidth-in optimizasiyası
Load-un paylaşdırılması
High availability
DDoS protection
Global reach

CDN İş Prinsipi

Traditional vs CDN

CDN Request Flow

CDN Architecture

PoP (Point of Presence)

PoP - CDN şəbəkəsinin bir coğrafi location-dakı physical datacenter-i.

CDN Components

Cache Strategies

1. Cache Headers

HTTP Cache Headers:

HTTP/1.1 200 OK
Content-Type: image/jpeg
Cache-Control: public, max-age=31536000
Expires: Thu, 31 Dec 2025 23:59:59 GMT
ETag: "33a64df551425fcc55e4d42a148795d9f25f89d4"
Last-Modified: Wed, 21 Oct 2023 07:28:00 GMT

Cache-Control Directives:

Directive	Məna
`public`	Hər kəs cache edə bilər (CDN, browser)
`private`	Yalnız browser cache edə bilər
`no-cache`	Revalidation tələb olunur
`no-store`	Heç cache edilməməlidir
`max-age=3600`	1 saat cache et
`s-maxage=7200`	Shared cache (CDN) üçün 2 saat
`must-revalidate`	Expire olduqda mütləq yoxla
`immutable`	Heç vaxt dəyişməyəcək

2. Cache Levels

3. Cache Key

Cache key - content-in cache-də unique identifikatorudur.

cache_key = hash(
    scheme +           // https
    host +             // example.com
    path +             // /images/logo.png
    query_params +     // ?width=100&quality=high
    custom_headers     // Accept-Language, Cookie (optional)
)

Example:

GET /api/users?page=2&limit=10
Accept-Language: en-US
Cookie: session=abc123

Cache Key: https://example.com/api/users?page=2&limit=10

4. Cache Invalidation

Problem: Content dəyişdikdə köhnə cache təmizlənməlidir.

Invalidation Methods:

Purge (Hard Delete)

# Delete specific file
curl -X PURGE https://cdn.example.com/images/logo.png

# Purge by tag
curl -X POST https://api.cdn.com/purge \
  -d '{"tags": ["homepage", "products"]}'

Soft Purge (Mark as stale)

# Mark as stale, revalidate on next request
curl -X PURGE https://cdn.example.com/images/logo.png \
  -H "Fastly-Soft-Purge: 1"

TTL Expiration

Cache-Control: max-age=3600  # Auto-expire after 1 hour

Versioning

# Old: /assets/style.css
# New: /assets/style.v2.css
# Or:  /assets/style.css?v=2

5. Cache Hit Ratio

Məqsəd: Cache-dən cavab verə bilmə nisbəti.

Cache Hit Ratio = (Cache Hits / Total Requests) × 100%

Example:
1000 requests total
800 served from cache (hits)
200 from origin (misses)

Hit Ratio = (800 / 1000) × 100% = 80%

Optimization:

Longer TTL
Better cache key design
Prewarming cache
Origin shield

CDN Content Types

1. Static Content

Perfect for CDN:

Images (JPEG, PNG, WebP)
CSS, JavaScript files
Fonts
Videos (VOD)
Documents (PDF)

# CDN configuration for static files
location ~* \.(jpg|jpeg|png|gif|ico|css|js|svg|woff2)$ {
    expires 1y;
    add_header Cache-Control "public, immutable";
}

2. Dynamic Content

Cacheable with conditions:

API responses (with proper headers)
Personalized content (with Vary header)
HTML pages (with ESI)

# API response with cache
HTTP/1.1 200 OK
Cache-Control: public, max-age=300, s-maxage=600
Vary: Accept-Encoding, Accept-Language

3. Streaming Content

Live və VOD:

Streaming Protocols:

HLS (HTTP Live Streaming) - Apple
DASH (Dynamic Adaptive Streaming) - Standard
RTMP - Legacy live streaming

Edge Computing

Edge Computing - CDN edge server-lərində kod icra etmək.

Edge Functions Use Cases

1. Image Optimization

// Cloudflare Worker - Image resize
addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})

async function handleRequest(request) {
  const url = new URL(request.url)
  const width = url.searchParams.get('width') || 800
  
  // Fetch original image
  const response = await fetch(url.origin + url.pathname)
  
  // Resize using Cloudflare Image Resizing
  return new Response(response.body, {
    headers: {
      ...response.headers,
      'cf-image-width': width,
      'cache-control': 'public, max-age=31536000'
    }
  })
}

2. A/B Testing

// Edge A/B testing
addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})

async function handleRequest(request) {
  const cookie = request.headers.get('cookie')
  
  // Assign variant
  let variant = 'A'
  if (cookie && cookie.includes('variant=B')) {
    variant = 'B'
  } else if (Math.random() < 0.5) {
    variant = 'B'
  }
  
  // Fetch variant-specific content
  const url = new URL(request.url)
  url.pathname = `/variant-${variant}${url.pathname}`
  
  const response = await fetch(url)
  
  // Set cookie
  const newResponse = new Response(response.body, response)
  newResponse.headers.set('Set-Cookie', `variant=${variant}; Path=/; Max-Age=86400`)
  
  return newResponse
}

3. Authentication

// Edge authentication
addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})

async function handleRequest(request) {
  const token = request.headers.get('Authorization')
  
  if (!token) {
    return new Response('Unauthorized', { status: 401 })
  }
  
  // Verify JWT at edge
  const isValid = await verifyJWT(token)
  
  if (!isValid) {
    return new Response('Invalid token', { status: 403 })
  }
  
  // Forward to origin
  return fetch(request)
}

4. Geolocation Routing

// Route based on location
addEventListener('fetch', event => {
  event.respondWith(handleRequest(event.request))
})

async function handleRequest(request) {
  const country = request.cf.country // Cloudflare provides this
  
  let origin
  switch(country) {
    case 'JP':
    case 'CN':
    case 'KR':
      origin = 'https://asia.example.com'
      break
    case 'GB':
    case 'DE':
    case 'FR':
      origin = 'https://eu.example.com'
      break
    default:
      origin = 'https://us.example.com'
  }
  
  const url = new URL(request.url)
  url.host = new URL(origin).host
  
  return fetch(url)
}

CDN Security

1. DDoS Protection

2. WAF (Web Application Firewall)

Protection against:

SQL Injection
XSS (Cross-Site Scripting)
CSRF
Bot traffic
Bad user agents

# WAF Rule example
rules:
  - id: block_sql_injection
    pattern: (?i)(union|select|insert|update|delete|drop).*from
    action: block
    
  - id: rate_limit_api
    path: /api/*
    limit: 100 req/minute
    action: challenge
    
  - id: block_bad_bots
    user_agent: (curl|wget|python-requests)
    action: block

3. Token Authentication

Signed URLs:

import hmac
import hashlib
import time

def generate_signed_url(base_url, secret_key, expiration=3600):
    expires = int(time.time()) + expiration
    
    # Create signature
    message = f"{base_url}{expires}"
    signature = hmac.new(
        secret_key.encode(),
        message.encode(),
        hashlib.sha256
    ).hexdigest()
    
    # Build URL
    return f"{base_url}?expires={expires}&signature={signature}"

# Example
url = generate_signed_url(
    "https://cdn.example.com/video.mp4",
    "my-secret-key",
    3600  # 1 hour
)
print(url)
# https://cdn.example.com/video.mp4?expires=1698765432&signature=abc123...

Validation at CDN:

// Validate signed URL
function validateSignedURL(request, secretKey) {
  const url = new URL(request.url)
  const expires = url.searchParams.get('expires')
  const signature = url.searchParams.get('signature')
  
  // Check expiration
  if (parseInt(expires) < Date.now() / 1000) {
    return false
  }
  
  // Verify signature
  const message = url.origin + url.pathname + expires
  const expectedSignature = hmac_sha256(message, secretKey)
  
  return signature === expectedSignature
}

4. HTTPS Everywhere

Benefits:

Data encryption
MITM protection
SEO boost
HTTP/2 support

CDN Performance Optimization

1. HTTP/2 & HTTP/3

HTTP/2:

Multiplexing
Header compression
Server push

HTTP/3 (QUIC):

UDP-based
Faster connection
Better mobile performance

2. Compression

# Brotli compression (better than gzip)
brotli on;
brotli_comp_level 6;
brotli_types text/plain text/css application/javascript application/json;

# Gzip fallback
gzip on;
gzip_types text/plain text/css application/javascript;

Compression Ratios:

Text files: 70-90% reduction
JavaScript: 60-80% reduction
Images (already compressed): 0-10%

3. Image Optimization

Automatic optimization:

<!-- Cloudflare Polish / Cloudinary -->
<img src="https://cdn.example.com/image.jpg" 
     srcset="https://cdn.example.com/image.jpg?w=400 400w,
             https://cdn.example.com/image.jpg?w=800 800w,
             https://cdn.example.com/image.jpg?w=1200 1200w"
     sizes="(max-width: 600px) 400px, (max-width: 1000px) 800px, 1200px">

4. Prefetching & Preloading

<!-- DNS prefetch -->
<link rel="dns-prefetch" href="https://cdn.example.com">

<!-- Preconnect -->
<link rel="preconnect" href="https://cdn.example.com">

<!-- Preload critical resources -->
<link rel="preload" href="https://cdn.example.com/main.css" as="style">
<link rel="preload" href="https://cdn.example.com/app.js" as="script">

<!-- Prefetch next page -->
<link rel="prefetch" href="https://cdn.example.com/next-page.html">

CDN Analytics & Monitoring

Key Metrics:

Monitoring Dashboard:

┌─────────────────────────────────────┐
│ CDN Performance Dashboard           │
├─────────────────────────────────────┤
│ Requests/sec:        45,000         │
│ Bandwidth:           2.5 GB/s       │
│ Cache Hit Ratio:     87%            │
│ Avg Latency:         45ms           │
│ P95 Latency:         120ms          │
│ Origin Requests:     5,850/s        │
│ Error Rate:          0.02%          │
├─────────────────────────────────────┤
│ Top Locations:                      │
│  🌍 US:     35%                     │
│  🌍 EU:     28%                     │
│  🌍 Asia:   25%                     │
│  🌍 Other:  12%                     │
└─────────────────────────────────────┘

Popular CDN Providers

Cloudflare

Xüsusiyyətlər:

300+ PoPs worldwide
Free tier available
DDoS protection included
Edge workers (serverless)
WAF
Analytics

Use cases:

Websites
APIs
Video streaming

AWS CloudFront

Xüsusiyyətlər:

AWS ecosystem integration
Lambda@Edge
450+ PoPs
Pay-as-you-go
Origin shield

Use cases:

AWS-hosted applications
S3 static websites
Video streaming

Fastly

Xüsusiyyətlər:

Instant purge (150ms)
VCL (Varnish) configuration
Real-time analytics
Edge compute
Advanced caching

Use cases:

High-traffic sites
Real-time applications
Media delivery

Akamai

Xüsusiyyətlər:

Largest CDN (300,000+ servers)
Enterprise-focused
Advanced security
IoT support

Use cases:

Enterprise applications
Large-scale streaming
Gaming

Others

Azure CDN - Microsoft ecosystem
Google Cloud CDN - GCP integration
KeyCDN - Budget-friendly
BunnyCDN - Performance-focused
StackPath - Edge computing

CDN Configuration Example

Cloudflare Page Rules

page_rules:
  - name: cache_static
    url_pattern: example.com/static/*
    settings:
      cache_level: Cache Everything
      edge_cache_ttl: 1 month
      browser_cache_ttl: 1 day

  - name: api_caching
    url_pattern: example.com/api/v1/products
    settings:
      cache_level: Cache Everything
      edge_cache_ttl: 5 minutes
      bypass_cache_on_cookie: session=*

  - name: no_cache_admin
    url_pattern: example.com/admin/*
    settings:
      cache_level: Bypass

NGINX Origin Configuration

server {
    listen 80;
    server_name origin.example.com;
    
    # Only allow CDN IPs
    allow 103.21.244.0/22;  # Cloudflare IPs
    deny all;
    
    location /static/ {
        root /var/www;
        
        # Cache headers
        expires 1y;
        add_header Cache-Control "public, immutable";
        
        # Security
        add_header X-Content-Type-Options "nosniff";
        add_header X-Frame-Options "DENY";
    }
    
    location /api/ {
        proxy_pass http://backend;
        
        # Vary header for proper caching
        add_header Vary "Accept-Encoding, Accept-Language";
        
        # Cache control
        add_header Cache-Control "public, max-age=300";
    }
}

Multi-CDN Strategy

Məqsəd: Bir neçə CDN provider istifadə etmək.

Benefits:

No vendor lock-in
Better global coverage
Failover capability
Cost optimization
Performance comparison

Best Practices

Caching Strategy:
- Set appropriate TTLs
- Use cache tags
- Implement versioning
- Monitor hit ratio (target: 80%+)
Security:
- Always use HTTPS
- Enable WAF
- Implement rate limiting
- Use signed URLs for private content
Performance:
- Enable compression (Brotli/Gzip)
- Use HTTP/2 or HTTP/3
- Optimize images
- Minimize origin requests
Monitoring:
- Track cache hit ratio
- Monitor latency (P50, P95, P99)
- Alert on high error rates
- Analyze geographic performance
Cost Optimization:
- Increase cache hit ratio
- Use origin shield
- Compress content
- Right-size TTLs
- Consider multi-CDN for arbitrage
Origin Protection:
- Restrict access to CDN IPs only
- Implement rate limiting
- Use origin shield
- Configure proper health checks

Troubleshooting

Common Issues:

1. Low Cache Hit Ratio:

Check TTL values
Verify cache headers
Look for query string issues
Review Vary headers

2. High Latency:

Check origin performance
Verify PoP proximity
Look for cache misses
Analyze TCP/SSL handshake

3. Stale Content:

Purge cache
Check TTL expiration
Verify Last-Modified headers
Implement cache invalidation

4. Origin Overload:

Enable origin shield
Increase TTLs
Implement rate limiting
Scale origin servers

Əlaqəli Mövzular

Load Balancing
HTTP/HTTPS Protocols
Caching Strategies
DNS and GeoDNS
DDoS Protection
Image Optimization
Video Streaming
Edge Computing
Web Performance Optimization

CDN Nədir?​

CDN İş Prinsipi​

Traditional vs CDN​

CDN Request Flow​

CDN Architecture​

PoP (Point of Presence)​

CDN Components​

Cache Strategies​

1. Cache Headers​

2. Cache Levels​

3. Cache Key​

4. Cache Invalidation​

Purge (Hard Delete)​

Soft Purge (Mark as stale)​

TTL Expiration​

Versioning​

5. Cache Hit Ratio​

CDN Content Types​

1. Static Content​

2. Dynamic Content​

3. Streaming Content​

Edge Computing​

Edge Functions Use Cases​

1. Image Optimization​

2. A/B Testing​

3. Authentication​

4. Geolocation Routing​

CDN Security​

1. DDoS Protection​

2. WAF (Web Application Firewall)​

3. Token Authentication​

4. HTTPS Everywhere​

CDN Performance Optimization​

1. HTTP/2 & HTTP/3​

2. Compression​

3. Image Optimization​

4. Prefetching & Preloading​

CDN Analytics & Monitoring​

Popular CDN Providers​

Cloudflare​

AWS CloudFront​

Fastly​

Akamai​

Others​

CDN Configuration Example​

Cloudflare Page Rules​

NGINX Origin Configuration​

Multi-CDN Strategy​

Best Practices​

Troubleshooting​

Əlaqəli Mövzular​

CDN Nədir?

CDN İş Prinsipi

Traditional vs CDN

CDN Request Flow

CDN Architecture

PoP (Point of Presence)

CDN Components

Cache Strategies

1. Cache Headers

2. Cache Levels

3. Cache Key

4. Cache Invalidation

Purge (Hard Delete)

Soft Purge (Mark as stale)

TTL Expiration

Versioning

5. Cache Hit Ratio

CDN Content Types

1. Static Content

2. Dynamic Content

3. Streaming Content

Edge Computing

Edge Functions Use Cases

1. Image Optimization

2. A/B Testing

3. Authentication

4. Geolocation Routing

CDN Security

1. DDoS Protection

2. WAF (Web Application Firewall)

3. Token Authentication

4. HTTPS Everywhere

CDN Performance Optimization

1. HTTP/2 & HTTP/3

2. Compression

3. Image Optimization

4. Prefetching & Preloading

CDN Analytics & Monitoring

Popular CDN Providers

Cloudflare

AWS CloudFront

Fastly

Akamai

Others

CDN Configuration Example

Cloudflare Page Rules

NGINX Origin Configuration

Multi-CDN Strategy

Best Practices

Troubleshooting

Əlaqəli Mövzular