Server 2012 R2 Active Directory Domain SRV dns records suddenly disappeared

1. Restart the Netlogon service on one of the Domain Controllers

OR

2. Run DCDiag /fix

OR

3. Manually create the records from the netlogon.dns file from one of the Domain Controllers

It's unusual for DNS records to be deleted (unless a person deleted them). Usually they are dnsTombstoned, so the records may still appear if using another tool like ADSIEdit even if not visible in DNS Manager or nslookup.

There are edge cases where scavenging can cause this (and a lot of other problems if scavenging is not configured properly).

http://blogs.technet.com/b/askpfeplat/archive/2012/07/09/the-case-of-the-missing-srv-records.aspx

http://blogs.technet.com/b/ad/archive/2008/08/08/a-complicated-scenario-regarding-dns-and-the-dc-locator-srvs.aspx