Hello,
I have this issue when migrating a 6.0 vCenter to 6.5:
Error
Host name vS-vCenter1.dpsi.jp is not DNS resolvable, but matches the machine certificates. If you do not configure a valid DNS resolvable hostname mapping, then you might not be able to connect to the vCSA afterwards
Resolution
Either update appliance /etc/hosts or /etc/resolv.conf file to properly access DNS servers or update appliance DNS servers with the proper host name mapping. To check if DNS server has record about local host name, execute `dig vS-vCenter1.dpsi.jp +short` locally on the appliance, or `nslookup vS-vCenter1.dpsi.jp` on a windows machine.
The commands suggested work as expected, and DNS records all resolve correctly.
What could the issue be?