A record vs CNAME record: differences and when to use each

An A record maps a name directly to an IPv4 address (AAAA does the same for IPv6). A CNAME record makes a name an alias of another name: the resolver restarts the lookup at the target and returns the target's addresses. Use A/AAAA when you control the IP address; use CNAME to point a subdomain at a host name someone else manages (a CDN, a SaaS app, a load balancer whose IPs change). A CNAME cannot coexist with any other record on the same name, so it cannot be used at the zone apex (example.com itself).

Side by side

The "CNAME and other data" rule

A name with a CNAME must have no other data. Zone tools reject the conflict; here dnspython parses three small zones:

cat > zones.py <<'EOF'
import dns.zone
base = """$ORIGIN example.com.
$TTL 3600
@    IN SOA ns1 hostmaster 1 7200 3600 1209600 3600
@    IN NS  ns1
@    IN A   192.0.2.10
ns1  IN A   192.0.2.53
www  IN CNAME @
"""
print("www as alias:", dns.zone.from_text(base).find_rdataset("www", "CNAME"))
for label, extra in [("www CNAME plus A", "www IN A 192.0.2.11\n"), ("CNAME at the apex", "@ IN CNAME lb.example.net.\n")]:
    try:
        dns.zone.from_text(base + extra)
    except Exception as e:
        print(f"{label}: {type(e).__name__}: {e}")
EOF
uv run -q --no-project --python 3.13 --with dnspython==2.8.0 python zones.py

www as alias: 3600 IN CNAME @
www CNAME plus A: CNAMEAndOtherData: rdataset type is not compatible with a CNAME node
CNAME at the apex: CNAMEAndOtherData: CNAME rdataset is not compatible with a regular data node

BIND reports the same conflict as CNAME and other data when loading a zone.

Pointing the apex at a host name

Because the apex cannot be a CNAME, providers offer workarounds:

• ALIAS / ANAME / CNAME flattening (provider-specific): you enter a host name, the provider's servers resolve it and answer with A/AAAA records. It is not a standard record type.
• HTTPS / SVCB records (RFC 9460) can point the apex to another name for HTTPS clients that support them (current browsers), but A/AAAA records are still needed for everything else.
• Redirect the apex to www with an HTTP redirect and put the CNAME on www.

Common mistakes

• A CNAME on a name that also needs MX or TXT records (mail and domain verification break): use A/AAAA there instead.
• MX and NS records must point to names with A/AAAA records, not to CNAMEs (RFC 2181 section 10.3).
• A trailing dot matters in zone files: target.example.net. is absolute; without the dot, the zone origin is appended.