When a website reaches a certain stage of development, migration becomes almost inevitable. This might be due to insufficient server performance, unsuitable data center location, the need for higher security, business upgrades, or a change of cloud service provider. Among all migration stages, DNS resolution is often the most easily overlooked yet most likely to cause large-scale access failures. Many website owners encounter problems during migration such as "website inaccessible," "access abnormalities in some regions," and "data inconsistencies between the old and new sites," all essentially related to improper DNS resolution handling.

　　I. Why is DNS resolution indispensable for website migration?

　　Simply put, the role of DNS is to translate "human-readable domain names" into "IP addresses that servers can recognize." When users access a website, they don't directly access the server IP; instead, they first look up the IP address corresponding to the domain name through DNS, and then establish a connection with the server.

　　When you migrate your website, the most critical changes typically include: a change in server IP address, a change in the server's data center or region, or the use of a new CDN, load balancer, or proxy service.

　　Regardless of the change, DNS resolution is essential to inform the entire network: this domain name should now point to the new server. If DNS resolution is not handled properly, some users may access the old server, while others may access the new server, or even experience complete access failure.

　　II. Understanding the "Delay" of DNS Implementation

　　Many beginners, after modifying DNS resolution, immediately ask, "I've changed it, why is my website still using the old one?" This actually involves a core characteristic of DNS: caching.

　　DNS is not a real-time, network-wide synchronized system. It relies on multi-level caching, including local computer or mobile phone DNS caching, browser caching, ISP DNS server caching, and public DNS caching. The existence of these caches causes inconsistent implementation times for DNS changes across different regions and networks. This time is usually controlled by TTL (Time To Live), which can range from minutes to hours, or even more than 24 hours.

　　In website migration scenarios, failing to consider this issue beforehand can easily lead to situations where your website works normally, but users experience abnormal access; it works during the day but suddenly crashes at night; it works domestically but fails internationally, etc.

　　III. Pre-Migration Preparations for DNS Resolution

　　Before officially migrating your website, there are several things strongly related to DNS that must be addressed in advance.

　　First, confirm the current DNS resolution structure of your domain. Don't just focus on one A record; many websites actually include separate resolutions for www and the root domain, subdomain resolutions, email-related MX records, and subdomains used by CDN, object storage, and APIs. It's recommended to compile a complete list of current DNS records before migrating to avoid missing any records and causing functional abnormalities after the migration.

　　Second, lower the TTL value in advance. If the current TTL is 600 seconds, 1800 seconds, or even higher, it's recommended to adjust it to a lower value, such as 300 seconds or 120 seconds, 24 hours before the migration. This will result in faster cache refresh and significantly reduced access disruptions when you actually switch IPs.

　　It's important to note that TTL changes themselves take time to take effect, so always do this in advance, not as a last-minute action.

　　Ⅳ, During Migration: The Correct Approach to DNS Switching

　　In actual migration processes, many people make the mistake of changing the DNS first and then migrating the website. This is a very dangerous practice. A more reasonable order is:

1. New server environment deployment complete
2. Complete website program and database migration
3. Maintain consistency between old and new server content
4. Test new server IP access for normal operation
5. Finally, modify DNS resolution

　　At the DNS level, a smooth switch is recommended, not a "one-size-fits-all" approach. If possible, allow the old server to continue running for a period during the migration window to ensure normal access even if some users still resolve to the old IP.

　　For websites using CDN, pay special attention to whether the CDN origin IP has been updated, whether the CDN node cache needs to be refreshed, and whether there are multiple layers of DNS resolution (domain name → CDN → origin server).

　　If only the domain A record is changed but the CDN origin configuration is forgotten, the result is often abnormal access and difficult troubleshooting.

　　V. Avoiding DNS Risks of "Data Inconsistency Between Old and New Servers"

　　One of the most common problems caused by DNS caching is that some users still access the old server. If website content on the old server has stopped being updated, data inconsistencies will occur. For example, user-submitted forms may be lost, comments, orders, and registration information may be out of sync, and the data seen in the management backend may differ from what users actually see.

　　To avoid this, before the DNS changes are fully effective, it is recommended to set the old server to read-only mode, temporarily disable critical write functions, or uniformly write data to the new server programmatically. This step is especially important for business websites; otherwise, data problems are often more difficult to fix than access anomalies.

　　VI. Post-Migration: DNS Verification and Troubleshooting Methods

　　After modifying the DNS, do not rely solely on browser access to determine success. A more scientific approach is to verify from multiple angles.

　　You can confirm the resolution status in the following ways:

• Test using different network environments (China Mobile, China Unicom, China Telecom)
• Perform resolution queries using different DNS servers
• Check whether the domain name points to the new IP address in different regions

　　If you find that some regions still point to the old server, do not rush to repeatedly modify the DNS. This is usually not a resolution error, but rather the cache has not yet expired. Frequent modifications may cause greater chaos.

　　VII. Summary of Common DNS Migration Migration Migrations

　　In actual website migrations, the following misconceptions are very common:

　　First, focusing only on the main domain and ignoring subdomains. Many backend interfaces, image services, and download services use independent subdomains. If these are overlooked, "partial functionality will fail."

　　Second, setting the TTL too high but temporarily switching DNS can indefinitely prolong the downtime.

　　Third, deleting old DNS records too early can cause users who still have cached old records to experience direct access failures.

　　Fourth, neglecting non-website DNS records such as email and verification records can lead to email anomalies or certificate verification failures after the migration.

　　In summary: Website migration itself is not terrible; what is terrible is a lack of sufficient understanding and respect for DNS resolution. As long as you plan your TTL in advance, clarify the DNS structure, follow the correct switching order, and patiently observe the DNS resolution after the migration, most migrations can be completed smoothly and seamlessly. For novice website owners, understanding how DNS works will not only help you successfully complete a website migration but also save you a lot of trouble in future maintenance.