The stability of a corporate website is never solely guaranteed by the server; the key factors truly impacting user experience often lie hidden within the DNS resolution chain. Once DNS fails, regardless of server configuration or network speed, visitors will be unable to access the website. Therefore, more and more enterprises are prioritizing DNS disaster recovery, incorporating primary/backup DNS, intelligent line switching, and multi-line resolution strategies into their overall business continuity systems. Building a reliable DNS architecture not only ensures website stability under high concurrency scenarios but also reduces operational losses due to single points of failure.

　　When planning DNS disaster recovery, enterprises typically prioritize building a primary/backup DNS architecture. Traditionally, many websites rely on a single DNS service provider, meaning only one set of NS records provides authoritative resolution for the domain. If this platform experiences equipment failure or a regional network outage, all resolution requests will instantly fail, rendering the website completely inaccessible. The idea behind primary/backup DNS is very simple: add two sets of NS records from different service providers for the same domain, allowing them to simultaneously handle authoritative resolution. When the primary DNS resolution link is interrupted or the network becomes congested, the backup DNS will automatically take over the resolution without manual intervention and without interrupting user access.

　　Setting up a primary and backup DNS architecture is not complex, but some details require attention during configuration. Generally, it only requires adding NS records from both service providers in the domain registrar's backend. However, one point that enterprises often overlook is that the records of the primary and backup service providers must be synchronized; otherwise, the backup DNS may fail to switch over in time after the primary DNS record is updated. To ensure data consistency, enterprises typically prepare an automatic synchronization script to periodically push the latest resolution records through the official API. For example, a simple synchronization logic example for two DNS service providers can be used as follows:

records = get_dns_records(master_dns_api)
for record in records:
    update_dns_record(backup_dns_api, record)

　　While this synchronization logic is simplified, the underlying concept is complete—the primary and backup DNS servers must remain consistent to achieve true disaster recovery. For large enterprises, a GitOps approach can be used to centrally manage DNS resolution configurations, automatically synchronizing them to authoritative nodes across multiple service providers with each change to ensure consistency.

　　After establishing the primary and backup DNS servers, enterprises need to further consider network connectivity. The internet environment is complex, and issues such as cross-carrier access latency, international network congestion, and regional network failures are often more common than server failures. If a visitor's DNS request needs to be forwarded across provinces or carriers, even if the resolution is ultimately successful, latency will increase significantly. Therefore, a multi-line resolution strategy becomes a crucial component of a DNS disaster recovery system.

　　The core of multi-line resolution is to ensure that users from different regions and networks access the IP address most suitable for them. For example, users from China Telecom are prioritized to resolve to China Telecom servers, and users from China Mobile are prioritized to resolve to China Mobile lines, ensuring that every access request takes the shortest path. This not only improves access speed but also reduces the impact of a single line failure on all users. When a carrier experiences network instability, the intelligent network system automatically switches to a higher-quality node, ensuring continuous website accessibility.

　　Building multi-line DNS resolution relies on the network differentiation capabilities provided by intelligent DNS service providers, such as those offering services like China Telecom, China Unicom, China Mobile, CERNET, overseas lines, or even down to the province/region level. Enterprises typically create different A records for each network based on their main website's deployment structure. Assuming multiple nodes are already deployed across different networks, basic multi-line DNS resolution can be established using a method similar to the following:

www.example.com  1.1.1.1
www.example.com  2.2.2.2
www.example.com  3.3.3.3
www.example.com  4.4.4.4

　　In this way, when a server or network on a particular line fails, the impact is limited to users on that line, rather than affecting all requests across the network. More advanced systems can monitor the health of each node and automatically adjust line routing when anomalies are detected, automating disaster recovery switching at the DNS resolution level. For example, intelligent DNS probes port 80 of a server every few seconds; if multiple timeouts occur, the node is immediately removed from the DNS resolution results. The automatic removal and subsequent DNS switching does not change the record format; it simply replaces the results from the specific line with those from the healthy node. From the user's perspective, access speed is slower, but access is uninterrupted.

　　Besides optimizing DNS resolution by line, enterprises also need to consider deploying backup nodes across regions. If a large-scale failure occurs in the primary data center, simply relying on intelligent line scheduling is insufficient. True high availability requires multiple data sources across the country or even globally, with switching implemented through DNS policies. For example, when a domestic node becomes unavailable, the DNS system automatically switches traffic from China to an overseas backup node. Although speed is slightly reduced, business operations continue, preventing complete interruption.

　　These automated line decisions require TTL (Time To Live) settings. The longer the TTL (Time To Live), the harder it is to refresh DNS records quickly; the shorter the TTL, the more timely the switch, but the greater the burden on the DNS server. Enterprises typically use 300 seconds (5 minutes) as a compromise, ensuring rapid disaster recovery without placing excessive demands on the DNS server. In some scenarios, such as second-level disaster recovery, the TTL is adjusted to 30 seconds or even 10 seconds, but this requires ensuring the service provider can stably handle the load.

　　In DNS disaster recovery systems, there is another often overlooked strategy—multi-active DNS. Multi-active is not the simplest master-slave model, but rather returns multiple available nodes for the same domain name, allowing clients to choose the optimal path based on network conditions. When the number of nodes is sufficient and the system supports load balancing algorithms, the disaster recovery capabilities provided by a multi-active architecture surpass those of a simple master-slave switch. For example, when DNS returns multiple IPs simultaneously, the browser automatically tries to connect to the fastest target node. When one of these nodes becomes unavailable, the client automatically skips it and continues connecting to other nodes, achieving seamless switching.

　　Multi-active DNS is more suitable for large websites or business structures that have already been containerized or microservice-based. Compared to the traditional primary/backup model, multi-active DNS doesn't rely on "switchover" for disaster recovery, but rather on "redundancy" for high availability. In extreme cases, even if multiple nodes fail simultaneously, the website remains accessible as long as available nodes exist.

　　Implementing multi-active DNS or primary/backup DNS doesn't guarantee complete peace of mind; enterprises should also establish a monitoring system. DNS link monitoring includes NS availability, resolution latency, line health, and domain hijacking detection. When the system detects abnormal traffic or resolution fluctuations, it should automatically trigger alerts and even automatic repair scripts. Enterprises can also utilize global site monitoring services to periodically access the website from different regions and compare results to determine if certain regions have been affected by DNS failures. The more comprehensive the monitoring, the more reliable the disaster recovery switchover.

　　To achieve true DNS disaster recovery, enterprises cannot rely solely on a single DNS service provider, nor can they be satisfied with basic line resolution functionality. Primary/backup DNS architecture provides basic authoritative resolution redundancy, multi-line resolution strategies solve cross-network access quality issues, multi-active DNS improves node fault tolerance, and an intelligent monitoring system ensures stable resolution quality. By integrating these strategies into a comprehensive system, websites can maintain accessibility even in the face of complex network environments, ISP issues, service provider failures, and even regional disasters. DNS disaster recovery is not a one-time task but a continuous optimization process. Only when enterprises maintain their DNS architecture as a core infrastructure can they truly achieve high availability and provide stable, long-term support for their business.