A Record vs CNAME: When to Use Which

If you've ever configured DNS, you've probably wondered: should I use an A record or a CNAME record? Both point a domain to a destination, but they work very differently. Here's what you need to know.

What Is an A Record?

An A record (Address record) maps a domain name directly to an IPv4 address. It's the most fundamental DNS record type.

example.com.    A    93.184.216.34

When someone visits your domain, the A record tells DNS resolvers the exact IP address of the server hosting your website.

What Is a CNAME Record?

A CNAME record (Canonical Name record) maps a domain name to another domain name. It's essentially an alias.

www.example.com.    CNAME    example.com.
blog.example.com.   CNAME    mysite.hosting.com.

When a resolver encounters a CNAME, it follows the chain and looks up the target domain's A record to get the final IP address.

Key Differences

Feature	A Record	CNAME Record
Points to	IP address	Another domain name
Can be used at root/apex	Yes	No (with exceptions)
Can coexist with other records	Yes	No — a CNAME cannot share a name with other record types
Lookup speed	One lookup	Requires additional lookup(s)
Flexibility when IPs change	Must update manually	Automatically follows the target

When to Use an A Record

• Root/apex domain — You must use an A record (or AAAA for IPv6) for your root domain (example.com) since CNAME records are not allowed at the zone apex per the DNS specification.
• When you know the IP address — If your hosting provider gives you a static IP, use an A record.
• Performance-sensitive setups — A records resolve in one lookup, while CNAMEs require at least two.

When to Use a CNAME Record

• Subdomains pointing to third-party services — Services like GitHub Pages, Heroku, or AWS load balancers give you a hostname, not an IP. Use a CNAME.
• www subdomain — Point www.example.com to example.com with a CNAME, then use an A record on the root.
• When the IP might change — If the target service manages its own IPs, a CNAME automatically follows those changes.

The CNAME at Root Problem

One of the most common DNS mistakes is trying to use a CNAME at the root domain. The DNS specification (RFC 1034) prohibits this because a CNAME cannot coexist with other record types, and the root domain needs SOA and NS records.

Some DNS providers offer workarounds:

• Cloudflare — CNAME flattening (resolves the CNAME to an A record at the edge)
• AWS Route 53 — ALIAS records
• DNSimple — ALIAS records

Quick Decision Guide

Ask yourself: Am I pointing to an IP address or a hostname?

• IP address → A record
• Hostname → CNAME record (unless it's the root domain)

When in doubt, check your hosting provider's documentation. They'll usually tell you exactly which record type to use.