Example:
host 10.68.17.12
12.17.68.10.in-addr.arpa domain name pointer analytics203.analytics.eqiad.wmflabs. 12.17.68.10.in-addr.arpa domain name pointer ci-jessie-wikimedia-22792.contintcloud.eqiad.wmflabs.
Possibly when instances are destroyed the information isn't always making it to designate.