How Do I Handle Inaccurate Scheduling Caused by the CNAME Record Set Cache in the Default Lines?

Original DNS Record Sets

1. A CNAME record set with a default line
2. Record sets of other types (excluding CNAME), with a non-default line for each record set

Take the hwtest-example.com domain name as an example. DNS record sets are configured as follows.

Table 1 Original DNS record sets

Domain Name	Line Type	Record Set Type	Record Set Value
hwtest-example.com	Default line for China Telecom	AAAA	ff03:x:x:x:x:x:x:x
hwtest-example.com	Default line for China Telecom	A	1.x.x.x
hwtest-example.com	Default	CNAME	www.huaweicloud.com

Figure 1 DNS record sets

Cause Analysis for Inaccurate Scheduling

Solutions

1. Configure A and AAAA record sets for a subdomain of the domain name, with a non-default line.
2. Configure a CNAME record set for the domain name with a non-default line (which must be the same as the line type specified in 1) to map the domain name to the subdomain specified in the A and AAAA record sets.

Take hwtest-example.com as an example.

Configure A and AAAA record sets for www.hwtest-example.com (a subdomain of hwtest-example.com), with a China Telecom default line for each record set.

Then, configure a CNAME record set for hwtest-example.com to map it to www.hwtest-example.com.

• www.hwtest-example.com is only an example domain name. Select a second-level domain name that has no record sets configured based on your service requirements.
• You must add A and AAAA record sets before adding a CNAME record set. If you add a CNAME record set first, DNS resolution may be interrupted.
• The CNAME record set configured for the domain name remains unchanged.

Table 3 and Figure 2 show the optimized DNS record sets.

Table 3 Optimized DNS record sets

Domain Name	Line Type	Record Set Type	Record Set Value
hwtest-example.com	Default line for China Telecom	CNAME	www.hwtest-example.com
www.hwtest-example.com	Default line for China Telecom	AAAA	ff03:x:x:x:x:x:x:x
www.hwtest-example.com	Default line for China Telecom	A	1.x.x.x
hwtest-example.com	Default	CNAME	www.huaweicloud.com

Figure 2 Optimized DNS record sets

A CNAME record set with a default line and a CNAME record set with a non-default line are configured, and the two record sets have the same priority. If you request an MX or TXT record set with a non-default line and no record set of the corresponding type is configured, no response is returned. In this case, cache pollution will not occur and DNS scheduling will be accurate.