cluster2.server.eu has no CNAME records.
Question and response
Question
dig cluster2.server.eu. NS
Answer
The response has no answer records.
Authority
server.eu. 3599 SOA ns1.server.eu. postmaster.server.eu. 2025100203 28800 7200 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0