Qunar DNS System: Architecture, Features, and Operational Practices

DNS Definition

DNS (Domain Name System) is a core Internet service that maps domain names to IP addresses via a distributed database, allowing users to access websites without remembering numeric IP strings.

DNS Query Process

Understanding DNS principles and query steps is essential for maintaining the system; the article outlines a typical DNS query flow.

1. The user (via PC/mobile) asks the local DNS server for the IP of www.qunar.com. If known, the server returns it directly.

2. If not, the local server queries a root DNS server, which may not know the specific IP but knows the IP of the top‑level domain "com".

3. The root server returns the IP of the "com" DNS server.

4. The local server asks the "com" DNS server for www.qunar.com; the "com" server knows the IP of qunar.com.

5. The "com" server returns qunar.com’s IP to the local server.

6. The local server then queries the qunar.com DNS server, which finally knows the IP of www.qunar.com.

7. The qunar.com server returns that IP to the local server.

8. The local server returns the IP of www.qunar.com to the user.

9. The user accesses the web server using that IP.

10. The web server returns the requested data.

Qunar DNS System

Qunar's DNS system has undergone several architectural changes, evolving into an intelligent DNS platform.

Initial System

The early DNS management followed the typical master‑slave model: the DNS master updated records, notified slaves, and slaves applied the changes, reducing errors and speeding up propagation across multiple authorized domain servers.

DNSDB Management System

As Qunar’s services grew, manual configuration became insufficient. The DNSDB management system was built to automate domain creation via APIs, integrate load‑balancing, and provide a web interface for rapid domain and traffic‑export management, supporting over a thousand domains.

1. Automatic domain allocation for virtual machines through API calls.

2. Load‑balancer integration with DNSDB to auto‑create domains and forwarding rules via the portal platform.

3. A web management console enabling one‑click traffic‑export switching and recovery, ensuring high availability.

DNS View

DNS view, supported since BIND 9, returns different IP addresses based on the client’s source IP, enabling traffic distribution per ISP and reducing latency for overseas users by directing them to appropriate exits.

EDNS

EDNS (Extension Mechanisms for DNS) helps mitigate issues where users configure external resolvers (e.g., 8.8.8.8), which can cause view misidentification. By carrying the true client IP, EDNS improves traffic routing accuracy and works alongside DNSSEC for security.

HTTPDNS

HTTPDNS performs DNS resolution over HTTP/HTTPS, bypassing traditional DNS hijacking. Qunar has implemented its own HTTPDNS service, incorporating DNS view and EDNS capabilities.

Intelligent DNS Switching

To handle IDC or ISP outages, Qunar monitors carrier‑level metrics, sets alarm thresholds, and automatically switches traffic to alternative exits. Once the issue resolves, traffic reverts automatically, achieving minute‑level fault self‑healing.

Conclusion

Through continuous enhancements, Qunar has built an intelligent DNS management system that meets diverse business needs, leveraging widely adopted technologies. The sharing aims to inspire peers in operations and foster industry exchange.