Learn how Multi-CDN architectures leverage EDNS Client Subnet for intelligent traffic routing and why fast DNS propagation is critical for optimal performance
Multi-CDN is an architecture where content is distributed across multiple Content Delivery Network providers simultaneously. This approach maximizes availability, performance, and geographic coverage by intelligently routing users to the best-performing CDN based on real-time conditions.
If one CDN experiences an outage, traffic automatically routes to healthy CDNs
Users connect to the fastest CDN based on their location and network conditions
Balance traffic across CDNs based on commit levels and pricing tiers
Leverage each CDN's strengths in different geographic regions
Industry Fact: Major streaming services and e-commerce platforms typically use 3-5 CDN providers to ensure 99.99% availability and optimal performance worldwide.
EDNS Client Subnet (RFC 7871) is a DNS extension that includes part of the end-user's IP address in DNS queries. This enables authoritative DNS servers to make routing decisions based on the actual user's location rather than the recursive resolver's location.
Without ECS, users behind public DNS resolvers (8.8.8.8, 1.1.1.1) would all appear to come from the resolver's location, leading to suboptimal CDN selection.
Route users to CDN nodes with the best peering arrangements with their specific ISP.
Make routing decisions at the subnet level for enterprise networks with specific requirements.
Privacy Note: ECS only transmits a subnet prefix (typically /24 for IPv4 or /56 for IPv6), not the full IP address, balancing functionality with user privacy.
Multi-CDN routing decisions combine multiple data points to select the optimal CDN endpoint. Let's examine a real-world example:
Domain: cdn.example.com
User IP: 98.137.11.163 (via ECS)
Region: North America - United States - Virginia
ASN: 701 (Verizon)
User is in Virginia, so prioritize CDNs with strong East Coast presence
Check real-time performance metrics for ASN 701 (Verizon) across all CDNs
CDN-A has direct peering with Verizon in Ashburn, VA - optimal choice
CDN-A Ashburn PoP is at 45% capacity with 0.8ms processing time
Within monthly commit for CDN-A; would incur overage charges on CDN-B
Final Decision:
Route to CDN-A's Ashburn, VA PoP (IP: 151.101.1.140) based on optimal peering, low latency (2ms), and cost efficiency.
Multi-CDN architectures demand specific capabilities from DNS providers to function effectively:
When RUM data indicates performance degradation, DNS changes must propagate globally within seconds.
Every millisecond of DNS resolution directly impacts user experience.
Sophisticated routing logic based on multiple real-time factors.
Programmatic control for real-time traffic management.
Important: Traditional DNS providers with TTL-based caching and manual updates cannot support the dynamic requirements of Multi-CDN architectures. Choose providers specifically designed for real-time traffic management.
RUM data provides the intelligence layer for Multi-CDN decision-making by collecting real-time performance metrics from actual users.
// Example RUM beacon data
{
"timestamp": "2024-01-20T15:30:45Z",
"user": {
"ip_subnet": "98.137.11.0/24",
"asn": 701,
"geo": {
"country": "US",
"region": "VA",
"city": "Richmond"
}
},
"performance": {
"dns_lookup": 12,
"tcp_connect": 28,
"ssl_handshake": 45,
"ttfb": 156,
"download_time": 234,
"total_time": 475
},
"cdn": "cdn-a",
"pop": "iad01",
"cache_status": "HIT"
}Collect millions of RUM beacons per second via high-throughput streaming
Calculate P50, P90, P99 latencies per ASN/Region/CDN combination
Identify performance degradation using ML models and statistical analysis
Generate routing rules based on performance thresholds and business logic
Push routing changes to DNS provider via API in real-time
Performance Tip: Process RUM data using stream processing frameworks like Apache Flink or Kafka Streams to achieve sub-second decision latency.
; Example Multi-CDN DNS configuration cdn.example.com. 30 IN A 151.101.1.140 ; CDN-A (primary) cdn.example.com. 30 IN A 104.16.123.96 ; CDN-B (secondary) cdn.example.com. 30 IN A 13.224.160.65 ; CDN-C (tertiary) ; With traffic management rules: ; - ASN 701 (Verizon) → CDN-A (100%) ; - ASN 7922 (Comcast) → CDN-B (70%), CDN-C (30%) ; - Default → Round-robin all CDNs
Always use canary deployments for routing changes:
A major video streaming service implemented Multi-CDN with EDNS Client Subnet to serve 50 million users globally. Here's how they handle a specific scenario:
Live sports event with 5 million concurrent viewers in North America
99.95%
Availability
32ms
Avg Latency
0.02%
Buffering Rate
Multi-CDN architectures with EDNS Client Subnet enable intelligent traffic routing that maximizes performance, availability, and cost efficiency. Success requires:
By implementing these practices, organizations can deliver consistent, high-quality experiences to users regardless of their location or network conditions.