How to optimize CDN costs? What are the cost optimization strategies?

Necessity of CDN Cost Optimization

As business grows, CDN costs can become a significant expense for enterprises. Through reasonable cost optimization strategies, CDN usage costs can be significantly reduced while maintaining service quality.

CDN Cost Components

1. Traffic Fees

Billing methods:

• Pay-as-you-go traffic: Billing based on actual traffic used
• Bandwidth-based billing: Billing based on peak bandwidth
• Hybrid billing: Combination of traffic and bandwidth billing

Billing cycles:

• Monthly billing
• Quarterly billing
• Annual billing (usually with discounts)

2. Request Count Fees

Billing objects:

• HTTP requests
• HTTPS requests
• API requests

Billing method:

• Billing by number of requests
• Usually has free tier

3. Storage Fees

Billing objects:

• Edge storage
• Origin storage
• Backup storage

Billing method:

• Billing by storage capacity (GB/month)
• Billing by storage type (standard, infrequent access, archive)

4. Feature Fees

Billing features:

• HTTPS certificates
• WAF protection
• DDoS protection
• Edge computing
• Video processing

5. Other Fees

• Data transfer fees (cross-region)
• Technical support fees
• Custom development fees

Cost Optimization Strategies

1. Cache Optimization

Improve Cache Hit Rate

Goal: Cache hit rate >95%

Optimization methods:

1. Set TTL reasonably

http
# Static resources: Long TTL
Cache-Control: public, max-age=31536000, immutable

# Dynamic content: Short TTL
Cache-Control: public, max-age=60

# Non-cached content
Cache-Control: no-store

2. Optimize cache keys

nginx
# Ignore query parameters that don't affect content
proxy_cache_key "$scheme$request_method$host$uri";

3. Use versioning

shell
# Not recommended: Need to clear cache after update
style.css

# Recommended: Change URL when updating
style.v1.css
style.v2.css

Effects:

• Reduce origin pull traffic
• Reduce origin load
• Save bandwidth costs

Cache Warming

Strategies:

• Warm up before content release
• Warm up popular content
• Regularly warm up updated content

Example:

bash
# Warm up multiple URLs
for url in $(cat urls.txt); do
  curl -X POST "https://api.cdn.com/prefetch" \
    -H "Content-Type: application/json" \
    -d "{\"urls\": [\"$url\"]}"
done

2. Content Optimization

Image Optimization

Optimization methods:

1. Choose appropriate format

• JPEG: Suitable for photos
• PNG: Suitable for transparent images
• WebP: 30-50% smaller than JPEG/PNG
• AVIF: 20-30% smaller than WebP

2. Compress images

bash
# Compress using ImageMagick
convert input.jpg -quality 85 output.jpg

# Compress PNG using pngquant
pngquant --quality=65-80 input.png

3. Responsive images

html
<picture>
  <source srcset="image-800w.webp" type="image/webp" media="(max-width: 800px)">
  <source srcset="image-1200w.webp" type="image/webp">
  <img src="image-1200w.jpg" alt="Description">
</picture>

Effects: Reduce 50-70% of image traffic

Video Optimization

Optimization methods:

1. Choose appropriate codec

• H.264: Good compatibility
• H.265/HEVC: 50% smaller than H.264
• VP9: Open source, 40% smaller than H.264
• AV1: Latest standard, 60% smaller than H.264

2. Adaptive Bitrate (ABR)

json
{
  "streams": [
    {"bitrate": 500000, "resolution": "640x360"},
    {"bitrate": 1000000, "resolution": "854x480"},
    {"bitrate": 2000000, "resolution": "1280x720"},
    {"bitrate": 4000000, "resolution": "1920x1080"}
  ]
}

3. Use CDN video processing

javascript
// Process video using CDN edge
const processedVideo = await cdn.processVideo({
  input: 'original.mp4',
  output: 'compressed.mp4',
  codec: 'h265',
  bitrate: '2000k'
})

Effects: Reduce 40-60% of video traffic

Text Compression

Enable compression:

nginx
# Gzip compression
gzip on;
gzip_types text/plain text/css application/json application/javascript;

# Brotli compression (20-30% smaller than Gzip)
brotli on;
brotli_types text/plain text/css application/json application/javascript;

Effects: Reduce 60-80% of text content

3. Traffic Optimization

Reduce Unnecessary Requests

Methods:

1. Bundle resources

html
<!-- Not recommended: Multiple CSS files -->
<link rel="stylesheet" href="style1.css">
<link rel="stylesheet" href="style2.css">
<link rel="stylesheet" href="style3.css">

<!-- Recommended: Bundle into one CSS file -->
<link rel="stylesheet" href="styles.css">

2. Use sprite images

css
.sprite {
  background-image: url('sprite.png');
  background-repeat: no-repeat;
}

.icon1 {
  background-position: 0 0;
  width: 32px;
  height: 32px;
}

.icon2 {
  background-position: -32px 0;
  width: 32px;
  height: 32px;
}

3. Inline critical CSS

html
<style>
  /* Inline critical CSS */
  .critical { ... }
</style>

Use HTTP/2 or HTTP/3

Advantages:

• Multiplexing: Reduce number of connections
• Header compression: Reduce data transfer volume
• Server push: Proactively push resources

Configuration example:

nginx
listen 443 ssl http2;

4. Intelligent Routing Optimization

Geographic Routing

Strategy: Route users to nearest node

Configuration example:

nginx
geo $geo {
    default default;
    1.0.0.0/8 us-east;
    2.0.0.0/8 us-west;
    3.0.0.0/8 eu-west;
}

upstream cdn_us_east {
    server cdn-us-east-1.example.com;
}

upstream cdn_us_west {
    server cdn-us-west-1.example.com;
}

Effects: Reduce cross-region traffic costs

Cost-optimized Routing

Strategy: Prioritize lower-cost nodes

Implementation:

• Analyze costs of each node
• Configure node weights
• Dynamically adjust routing

5. Budget and Quota Management

Set Budget Limits

Methods:

• Set monthly budget limit
• Configure overage alerts
• Auto-degradation strategy

Configuration example:

javascript
// Set budget alert
const budget = {
  monthly: 10000, // $10,000
  alertThreshold: 0.8, // Alert at 80%
  stopThreshold: 1.0 // Stop service at 100%
}

function checkBudget(currentSpend) {
  const ratio = currentSpend / budget.monthly
  
  if (ratio >= budget.stopThreshold) {
    // Stop service or degrade
    enableDegradationMode()
  } else if (ratio >= budget.alertThreshold) {
    // Send alert
    sendAlert(`Budget usage: ${ratio * 100}%`)
  }
}

Use Reserved Instances

Strategy:

• Reserve bandwidth or traffic
• Get discounted prices
• Suitable for stable business

Example:

bash
# Purchase reserved instances
aws cloudfront create-reserved-instance \
  --reserved-instance-offering-id xxx \
  --instance-count 10

Effects: Save 20-40% of costs

6. Multi-CDN Strategy

Use Multiple CDN Providers

Advantages:

• Reduce single vendor risk
• Leverage strengths of each CDN
• Get better pricing

Implementation methods:

1. DNS load balancing

bash
# Configure CNAME for multiple CDNs
example.com.  IN  CNAME  cdn1.example.com
example.com.  IN  CNAME  cdn2.example.com

2. Intelligent routing

javascript
// Select CDN based on cost and performance
function selectCDN(userLocation, content) {
  const cdns = [
    { name: 'cdn1', cost: 0.01, performance: 0.8 },
    { name: 'cdn2', cost: 0.015, performance: 0.9 },
    { name: 'cdn3', cost: 0.008, performance: 0.7 }
  ]
  
  // Select optimal CDN based on business needs
  return cdns.reduce((best, cdn) => {
    const score = calculateScore(cdn, userLocation, content)
    return score > best.score ? { ...cdn, score } : best
  }, { score: 0 })
}

Allocate CDN by Content Type

Strategy:

• Static content: Use low-cost CDN
• Dynamic content: Use high-performance CDN
• Video: Use video-optimized CDN

Example:

javascript
// Select CDN based on content type
function selectCDNByContentType(contentType) {
  const cdnMapping = {
    'image/jpeg': 'low-cost-cdn',
    'video/mp4': 'video-optimized-cdn',
    'application/json': 'high-performance-cdn'
  }
  
  return cdnMapping[contentType] || 'default-cdn'
}

Cost Monitoring and Analysis

1. Cost Analysis Tools

CDN Built-in Analytics

Cloudflare Analytics:

• Traffic statistics
• Request analysis
• Cost reports

AWS Cost Explorer:

• Cost trend analysis
• Cost forecasting
• Cost optimization recommendations

2. Custom Cost Monitoring

Implementation example:

javascript
// Track CDN costs
const costTracker = {
  traffic: 0,
  requests: 0,
  storage: 0,
  
  addTrafficCost(bytes) {
    this.traffic += bytes * 0.00001 // $0.01 per GB
  },
  
  addRequestCost(count) {
    this.requests += count * 0.000001 // $0.001 per 1000 requests
  },
  
  addStorageCost(gb) {
    this.storage += gb * 0.02 // $0.02 per GB per month
  },
  
  getTotalCost() {
    return this.traffic + this.requests + this.storage
  }
}

// Usage example
costTracker.addTrafficCost(1024 * 1024 * 1024) // 1 GB
costTracker.addRequestCost(1000) // 1000 requests
costTracker.addStorageCost(100) // 100 GB

console.log(`Total cost: $${costTracker.getTotalCost()}`)

3. Cost Optimization Recommendations

Recommendations based on data analysis:

1. Identify high-cost content

sql
-- Query content with highest traffic
SELECT url, SUM(bytes) as total_bytes
FROM cdn_logs
WHERE date >= '2026-02-01'
GROUP BY url
ORDER BY total_bytes DESC
LIMIT 10;

2. Analyze cache hit rate

sql
-- Query content with low cache hit rate
SELECT url, 
       COUNT(*) as total_requests,
       SUM(CASE WHEN cache_status = 'HIT' THEN 1 ELSE 0 END) as hits,
       SUM(CASE WHEN cache_status = 'HIT' THEN 1 ELSE 0 END) / COUNT(*) * 100 as hit_rate
FROM cdn_logs
WHERE date >= '2026-02-01'
GROUP BY url
HAVING hit_rate < 80
ORDER BY hit_rate ASC
LIMIT 10;

3. Optimization recommendations

• Implement compression for high-cost content
• Optimize cache strategy for low hit rate content
• Use low-cost storage for infrequently accessed content

Cost Optimization Best Practices

1. Regular Cost Review

Review content:

• Monthly cost reports
• Cost trend analysis
• Optimization opportunity identification

2. A/B Testing

Test different strategies:

• Different cache strategies
• Different compression algorithms
• Different CDN configurations

3. Continuous Optimization

Optimization process:

1. Monitor cost data
2. Analyze cost composition
3. Implement optimization measures
4. Evaluate optimization effects
5. Continuous improvement

Interview Points

When answering this question, emphasize:

1. Understanding of CDN cost components
2. Mastery of multiple cost optimization strategies
3. Practical cost optimization experience
4. Ability to analyze and monitor CDN costs
5. Understanding of balance between cost and performance