When you connect your web service to Anti-DDoS, we recommend that you Access to Anti-DDoS Pro through CNAME rather than A record.
Advantages of using CNAME are as follows:
CNAME is more convenient to use. After you modify the resolution configuration once at your DNS service provider (such as Alibaba Cloud DNS or DNSPod), the change takes effect with no deployment and O&M efforts.
When the Anti-DDoS Pro on a line encounters an exception, domain names using CNAME resolution can be automatically switched to protection under another Anti-DDoS Pro line. For example, if the China Unicom line fails or is congested, the domain names may get auto scheduled to be protected under the China Telecom line.
If you are using a “China Telecom + China Unicom” two-line subscription, when the China Unicom line suffers from attacks and is thrown into the black hole, CNAME can automatically schedule domain name resolution to the China Telecom line, which avoids affecting services that are previously resolved to the China Unicom line.
You can check if your domain name is connected to Anti-DDoS Pro through CNAME on the Web Service page.
If the domain name is connected to Anti-DDoS Pro through CNAME, the Instance & ISP Line prompts CNAME access successful.
If the domain name is not connected to Anti-DDoS Pro through CNAME (for example, A record is used, or the CNAME resolution was incorrectly configured), the Instance & ISP Line prompts CNAME access failed.
Note: This prompt does not necessarily indicate that the domain name resolution or service encounters any exception. Domain names that cannot use CNAME resolution can be configured normally using A record.