I hit the following issue recently while creating a VCF 4.1 ‘NSX-T VI Workload Domain‘ for a VCF on VxRail solution:

Referring to the VMware VCF 4.0.1 Release Notes (extract):

VI workload domain creation or expansion operations fail

If there is a mismatch between the letter case (upper or lower) of an ESXi host’s FQDN and the FQDN used when the host was commissioned, then workload domain creation and expansion may fail.

Workaround: ESXi hosts should have lower case FQDNs and should be commissioned using lower case FQDNs.

https://docs.vmware.com/en/VMware-Cloud-Foundation/4.0.1/rn/VMware-Cloud-Foundation-401-Release-Notes.html

TROUBLESHOOTING STEPS

Perform a DNS Lookup (results look good):

Browse to vCenter HTML client and confirm ESXi hostname is ‘lower-case’ (results look good):

Finally I opened the DCUI console via iDRAC virtual session (culprit found):

Next step is to edit the Hostname from DCUI, re-entering as lower-case:

All set!:

Retrying the VI WLD workflow from SDDC Manager (SUCCESS!):