When using Route53 the Hosted Zone is often a subdomain for a domain managed using external DNS. In this case the external DNS must be updated to delegate management of the subdomain to your hosted zones name servers.
When you create a public Hosted Zone in Eucalyptus it will be allocated some nameservers. You can use the AWS CLI to determine the Name Servers for your zone:
# aws route53 list-hosted-zones
HOSTEDZONES 87a20e2b-f835-4775-a6ad-16f14033668a /hostedzone/ZAAKJGJPMUHV32 subdomain.example.com. 2
CONFIG False
#
# aws route53 list-resource-record-sets --hosted-zone-id ZAAKJGJPMUHV32 --query "ResourceRecordSets[?Type == 'NS']"
subdomain.example.com. 900 NS
RESOURCERECORDS ns1.mycloud.example.com.
To discover the nameservers, first list the hosted zone to find the identifer and then pass the identifer to list-resource-record-sets. The example above uses a query to output only the NS information.
The external DNS should be updated to add a Name Server NS record and a corresponding A record to map that name to an IP address:
subdomain.example.com NS ns1.mycloud.example.com.
ns1.mycloud.example.com A 1.X.Y.123
The external DNS must not have an SOA record for the delegated subdomain as your Hosted Zone in Eucalyptus Route53 is authoritative.