pagerduty has switched to AWS + 4 different root TLDS:
$ host -t NS pagerduty.com
pagerduty.com name server ns-219.awsdns-27.com.
pagerduty.com name server ns-739.awsdns-28.net.
pagerduty.com name server ns-1198.awsdns-21.org.
pagerduty.com name server ns-1569.awsdns-04.co.uk.
I think I'm satisfied.