Domain name resolution is a crucial part of the internet architecture, responsible for mapping domain names to corresponding IP addresses, ensuring users can access target websites or services. For many businesses and developers, subdomain distribution (i.e., configuring multiple subdomains under a main domain) is a common requirement. This method allows different services to be distributed across different subdomains, improving system flexibility and scalability while optimizing website or application performance.

　　We need to understand what subdomain distribution is. In the Domain Name System (DNS), domain names are hierarchically structured. Top-level domains (TLDs) are at the top level, such as ".com" and ".org"; second-level domains are located below the TLDs, usually what we call the main domain, such as "example.com". Under the main domain, multiple subdomains can be configured, such as "www.example.com" and "api.example.com", which can each point to different servers or services. This distribution method not only simplifies management but also allows each service to independently perform load balancing, access control, and other operations.

　　To implement subdomain distribution, you first need to configure domain name resolution. In a DNS management system, we can add different DNS records to point subdomains to different IP addresses or servers. Common DNS records include A records, CNAME records, and MX records. For subdomain distribution, we most commonly use A records and CNAME records.

　　An A record is the most basic DNS record; it maps a domain name to an IP address. When a user requests a domain name, the DNS server resolves the domain name to the corresponding IP address, thus finding the target server. If you want to point a subdomain to a specific IP address, using an A record is the most direct way. For example, suppose you want to point "api.example.com" to the IP address "192.168.1.1", you can add the following A record in the DNS management system:

api.example.com.    IN    A    192.168.1.1

　　A CNAME record is another common type of DNS record. Its purpose is to point a domain name to another domain name, rather than directly to an IP address. When using a CNAME record, the DNS server looks up the A record for the target domain name and then resolves the corresponding IP address. CNAME records are suitable for mapping a subdomain to another domain name, rather than directly pointing to an IP address. For example, if you want to point "blog.example.com" to "example.blog.com", you can use the following CNAME record:

blog.example.com.    IN    CNAME    example.blog.com.

　　In some cases, subdomain distribution may involve load balancing across multiple servers, or distributing a domain name to different regions or services. This can be achieved by setting multiple A records or CNAME records, or by using a load balancer in conjunction with these methods.

　　When you need to achieve load balancing across multiple servers, you can set multiple A records for the same subdomain, pointing to different IP addresses. For example, if you have two web servers located at "192.168.1.1" and "192.168.1.2" respectively, you can configure the following A record for "www.example.com":

www.example.com.    IN    A    192.168.1.1
www.example.com.    IN    A    192.168.1.2

　　DNS servers distribute requests using a round-robin method, ensuring traffic is distributed across multiple servers to achieve load balancing. It's important to note that DNS load balancing is a simple method suitable for applications with low traffic. If your application requires more advanced load balancing (e.g., based on traffic weights, geographic location), consider using a professional load balancing service or software.

　　When configuring second-level domain name distribution, several common security issues need to be considered. First, ensure DNS records are configured correctly to avoid domain names failing to resolve or pointing to the wrong server due to misconfiguration. Second, protect DNS servers from DNS attacks, especially DNS cache poisoning. To improve security, DNSSEC (DNS Security Extensions) can be used to prevent DNS data from being tampered with or forged. DNSSEC ensures the integrity and authenticity of DNS data by digitally signing DNS queries and responses.

　　Furthermore, pay attention to the DNS TTL (Time-to-Live) setting. TTL determines how long DNS records are stored in the cache. If the TTL is set too long, changes to domain name resolution may not take effect promptly; if the TTL is set too short, it may increase the burden of DNS queries and impact performance. Therefore, setting a proper TTL value is crucial for ensuring efficient and reliable domain name resolution.

　　In actual domain name resolution configuration, specific services or technologies may also be involved, such as CDN (Content Delivery Network) and firewall configuration. If you use a CDN to accelerate website content distribution, you can point the DNS records of your subdomains to the domains provided by the CDN, instead of directly pointing them to your server. This helps improve website performance and increase security.

　　In summary, configuring domain name resolution for subdomain distribution is a relatively simple process, but it requires consideration of several factors, including DNS record type, load balancing, security, and TTL settings. Correctly configuring these items can effectively improve website performance, scalability, and security. Through proper domain name distribution, independent access points can be provided for different services, making websites or applications more flexible and efficient in daily operations.

　　Frequently Asked Questions:

　　Q1: Why can't my subdomain resolve correctly?

　　A1: Possible reasons include incorrect DNS record configuration, DNS server failure, or outdated domain name resolution cache. You can check your DNS record settings to ensure they are correct and try clearing your local DNS cache or using a different DNS resolution server.

　　Q2: How to configure DNS records to achieve load balancing?

　　A2: You can distribute traffic to multiple IP addresses by setting multiple A records for the same subdomain, or use CNAME records to point the subdomain to a single load balancer.

　　Q3: Can different TTL values ​​be configured for different subdomains?

　　A3: Yes, each DNS record can have its own TTL value, allowing you to adjust the cache time according to different needs. For example, for frequently changing subdomains, a shorter TTL value can be set.

　　Q4: How to prevent DNS attacks?

　　A4: You can enable DNSSEC to sign DNS queries and responses, ensuring the security of DNS data. In addition, regularly checking DNS records and monitoring abnormal traffic are also effective measures to prevent attacks.