u1.amazonaws.com has no CNAME records.
Question and response
Question
dig u1.amazonaws.com. NS
Answer
The response has no answer records.
Authority
amazonaws.com. 900 SOA dns-external-route53.us-east-1.amazonaws.com. hostmaster.amazon.com. 2017224478 180 60 604800 900
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0