CNAMErecord

CNAMErecord is a type of resource record in the Domain Name System (DNS) that maps an alias name to an authoritative hostname. When a DNS resolver encounters a CNAMErecord, it replaces the alias with the canonical name specified in the record and continues the lookup using that name. This mechanism allows multiple domain names to point to the same underlying host without duplicating A or AAAA records.

A CNAMErecord is defined in the DNS zone file using the syntax "alias IN CNAME canonical.example.com." Only one CNAMErecord can exist for a given domain name, and it cannot coexist with other record types such as A, AAAA, or MX for that name. In practice, CNAMErecords are often used for subdomains, for example, www.example.com pointing to example.com, or for creating aliases in service registries like s3.amazonaws.com/dest.

CNAMErecords are limited in that they incur an additional DNS query step, which can add latency. Additionally, because they delegate DNS resolution, they can result in longer response times if the canonical name resolves to a host in a distant zone. Despite these limitations, CNAMErecords are essential for simplifying domain management, enabling flexible hosting arrangements, and supporting dynamic redirection of services across domain names.