Add CNAME record to DNS when A-record exists?

Solution 1:

CNAME record must exist only on its own. You can not have a zone data like:

name A xx.xx.xx.xx
name CNAME othername

Some special records may coexist with CNAME, to attest it is authentic. DNSSEC specification mandates a use of RRSIG and NSEC for the purpose of authentication, which can coexist with CNAME, see RFC 4034 section 3 and RFC 4034 section 4. There are older specifications, RFC 2181, section 10.1, RFC 2535 section 2.3.5, which say the same for SIG, NXT and KEY records.

All end application data must be attached to the RR which is the CNAME target; see RFC1034 section 3.6.2 (the original DNS specification).

some.name.tld CNAME rec.othername.tld
rec.othername.tld A xx.xx.xx.xx
rec.othername.tld TXT text-rr-data

Also note, that CNAME label inherits not only A (address), but many other features of target label, notably TXT.

This (older) RFC also contains the harder version of above restriction which was lifted for DNSSEC:

If a CNAME RR is present at a node, no other data should be present; this ensures that the data for a canonical name and its aliases cannot be different.

Without DNSSEC, this harder restriction effectively still applies.