4. Traffic Scheduling: Getting Users to the "Nearest" Node

4.1 Intelligent DNS Scheduling

Traditional DNS resolution:

User asks: What's the IP for cdn.example.com?
DNS answers: 1.2.3.4 (fixed)

Intelligent DNS resolution:

User (Beijing Unicom) asks: What's the IP for cdn.example.com?
Intelligent DNS: Let me check... Beijing Unicom's CDN node is 1.2.3.4

User (Shanghai Telecom) asks: What's the IP for cdn.example.com?
Intelligent DNS: Shanghai Telecom's CDN node is 5.6.7.8

Scheduling Dimensions:

Dimension	Description	Effect
Geographic Location	Assign by province/city/country	Nearby access, reduced latency
ISP	Unicom/Telecom/Mobile/BGP	Same-ISP transmission, avoid cross-ISP
Node Load	Real-time CPU/bandwidth/QPS	Avoid overloaded nodes
Node Health	Availability probing	Auto-remove faulty nodes
Cost Factors	Bandwidth unit price differences	Balance performance and cost

4.2 HTTP DNS and Direct IP Connection

Traditional DNS has a problem: DNS hijacking and resolution latency.

HTTP DNS Solution:

Client → Bypasses system DNS → Directly queries HTTP DNS service (e.g., 223.5.5.5:80)
         ↓
    Returns optimal IP list (with weights)
         ↓
    Client probes network quality and selects the best IP

Advantages:

• Anti-hijacking: bypasses ISP DNS
• More precise: can select IP based on client network quality
• Real-time: faster failover

Practical Recommendations:

• Mobile apps are strongly recommended to integrate HTTP DNS
• Web apps can use CNAME-based scheduling provided by CDN
• Critical services can implement multi-IP failover (one domain returns multiple IPs)