What is a DNS CNAME record?

A Canonical Name (CNAME) record is a type of resource record in the Domain Name System (DNS) that maps one domain name to another.

There are various types of DNS records. In most cases, a CNAME record works with an A record. The following section describes A records.

A record

An address record (A record) is a mapping record that maps a domain name to an IP address.

When you access a domain name, the DNS server uses the A record to resolve the domain name to the mapped IP address. Then, you can access the domain name by using the IP address.

Example:

Record type              Domain name                      Record value 
A               www.example.com            10.10.10.10

CNAME record

Compared with an A record, a CNAME record maps a domain name to another domain name, which can be considered an alias. A CNAME record value can be mapped to a specific server through an A record.

Example:

Record type      Domain name                             Record value 
CNAME       cname1.example.com               www.example.com.w.kunlunsl.com
A           www.example.com.w.kunlunsl.com   10.10.10.10

When you access the domain name cname1.example.com, the DNS server obtains the CNAME record value www.example.com.w.kunlunsl.com. Based on the A record of www.example.com.w.kunlunsl.com, the domain name cname1.example.com is resolved to the IP address 10.10.10.10.

Note

You cannot have an A record and CNAME record for the same hostname.

Benefits of DNS CNAME records

Quickly update server IP addresses

When the IP address of a server changes, such as from 10.10.10.10 to 10.10.10.1, you only need to change the value of the A record to the new IP address 10.10.10.1. This way, you can point three domain names to the new IP address without the need to modify the CNAME records of the domain names.

Before the server IP address changes:

Record type             Domain name                       Record value 
CNAME               cname1.example.com        www.example.com
CNAME               cname2.example.com        www.example.com
CNAME               cname3.example.com        www.example.com
A                   www.example.com           10.10.10.10

After the server IP address changes:

Record type             Domain name                       Record value 
CNAME               cname1.example.com        www.example.com
CNAME               cname2.example.com        www.example.com
CNAME               cname3.example.com        www.example.com
A                   www.example.com           10.10.10.1

Work with Alibaba Cloud CDN to accelerate the delivery of static resources

Alibaba Cloud CDN is a global network of points of presence (POPs) that are distributed across the globe. Alibaba Cloud CDN serves to reduce origin traffic. This in turn prevents network congestion and ensures that content is delivered with minimal latency across regions in various use cases. For more information, see What is Alibaba Cloud CDN?

The CNAME record value returned by Alibaba Cloud DNS in Step 3 is the CNAME assigned by Alibaba Cloud CDN to the domain name. You can reach the routing system of Alibaba Cloud CDN by accessing www.example.com.cname.com. Then, the routing system assigns an optimal POP based on the information of the user. This way, the user can obtain the resource from the POP so that the delivery of the resource is accelerated.