/etc/sudoers.d/designate_sudoers is in designate-common 2014.1-18+deb8u1.
This file is owned by root:root, with mode 0o440.
The actual contents of the file can be viewed below.
1 2 3 | Defaults:designate !requiretty
designate ALL = (root) NOPASSWD: /usr/sbin/rndc
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