Solutions for DNS resolution errors causing websites to be inaccessible

　　During website deployment and maintenance, "incorrect DNS resolution settings causing the website to be inaccessible" is a common problem encountered by many novice website owners. Even though the cloud server is running normally and the ports are open, entering the domain name in the browser still fails to access the site, sometimes even resulting in a "server not found" error. This situation is often not due to a problem with the server itself, but rather a configuration error in the DNS resolution process.

　　Simply put, the role of DNS is to translate domain names into server IP addresses. When a user accesses your website, the browser first queries the DNS for the IP address corresponding to the domain name, and then uses that IP address to connect to the cloud server. If the DNS record is misconfigured, or the resolution has not yet taken effect, the browser cannot find the correct server, and naturally, the website cannot be accessed. Therefore, DNS is the most crucial bridge between the domain name and the cloud server.

　　When you find that a website cannot be accessed via its domain name, the first step should be to check if the server itself is functioning correctly. You can directly enter the public IP address of the cloud server in the browser. If the page opens normally using the IP address, it means that the web service and server configuration are basically fine, and you can then focus your troubleshooting on the DNS. If even the IP address is inaccessible, prioritize checking the firewall, security groups, port listening, and web service status, rather than worrying about DNS settings.

　　After confirming the server is functioning correctly, log in to the domain management backend to check the DNS records. The most common mistake is entering an incorrect IP address in the A record. Some beginners mistakenly enter their internal IP address or copy an old server's address, causing the domain to point to a non-existent host. The correct approach is to enter the public IPv4 address of the cloud server, ensuring there are no extra spaces or symbols. Also, check that the host record is correct; typically, use "@" to access the main domain and "www" to access the www domain.

　　Besides incorrect IP addresses, choosing the wrong record type is also a common problem. Most websites require A records to directly point to the server IP, not CNAME records. Setting the root domain as a CNAME is not supported by some DNS providers, easily leading to resolution errors. Additionally, some website owners add multiple A records for the same hostname with different IP addresses, which can cause instability without load balancing.

　　After setting up the DNS records, it's crucial to pay attention to the DNS activation time. DNS doesn't take effect instantly; it undergoes synchronization across global caching nodes, typically taking anywhere from a few minutes to several hours. Frequent record modifications during this time can easily lead to different IP addresses resolving to different regions, resulting in websites being accessible in some places but not others. New website owners should patiently wait a while after modifying the DNS records before conducting a unified test.

　　To determine if the DNS resolution has taken effect, you can use tools like ping or nslookup. Execute ping the domain name in your local command line. If the returned IP matches the public IP address of the cloud server, the current network environment has successfully resolved the DNS. If they don't match, the cache hasn't been refreshed or there's still a configuration problem. You can also use online DNS lookup tools to simultaneously check the resolution results from multiple regions, which is very helpful for troubleshooting regional access anomalies.

　　Another easily overlooked point is the domain status. Some domains are newly registered and still locked or unverified. In this case, even if DNS records are added, the website will not be accessible. Some domain extensions also require real-name verification before DNS services can be enabled. If the DNS resolution configuration is correct but still ineffective, check if the domain name is in a normally active state.

　　In domestic cloud server environments, you may also encounter DNS poisoning or hijacking issues. This usually manifests as the local DNS resolving to an incorrect IP address or redirecting to an unfamiliar page. When encountering this problem, try changing your local DNS to 1.1.1.1 or 8.8.8.8 for testing. It is also recommended to enable HTTPS and configure a trusted certificate on the server side to reduce the risk of hijacking. If your business has high stability requirements, consider using an authoritative DNS service provider or enabling DNSSEC.

　　Some website owners configure CDN when deploying their websites, which also increases the complexity of DNS troubleshooting. When CDN is enabled, the domain name usually points to the CNAME address provided by the CDN, rather than directly to the server IP. If the CDN configuration is incomplete, or the origin address is entered incorrectly, the DNS may resolve normally, but the website will not open. In this case, you need to confirm in the CDN console that the origin IP, origin port, and protocol are correct, and ensure that the cloud server security group has allowed CDN node access. If you're using subdomains, such as api.example.com or blog.example.com, make sure each subdomain has its own DNS record. Many beginners only configure the main domain but forget about the subdomains, causing some functional modules to become inaccessible. It's recommended to compile a list of all necessary domains in advance when planning your website structure and configure them all at once to avoid omissions.

　　TTL settings also affect troubleshooting efficiency. TTL is the DNS cache time; the higher the value, the longer the DNS records are cached in various locations. For sites that frequently need to adjust their server IP, a smaller TTL, such as 300 seconds, can be set, making changes to the DNS records take effect more quickly. For stable websites, a larger TTL can be used to reduce the pressure on authoritative DNS queries.

　　In summary: When a website is inaccessible due to incorrect DNS settings, don't panic. Troubleshoot step-by-step in the following order: "Is the server working properly? Are the DNS records correct? Is the domain status valid? Is the DNS resolution effective? Are there any CDN or pollution factors?" Most problems can be traced back to these steps. As long as you understand the basic logic of DNS and master common detection methods, even a novice website owner can independently solve most DNS resolution problems.