vSphere Client, adding hosts requires name resolution locally
Although some people may find this obvious, it’s not something that everyone has experienced so I thought I should mention this requirement. This is especially true when setting up test labs or greenfield production systems where you are using the vSphere client on a separate workstation.
When first building your vSphere vCenter and adding the hosts ensure you create DNS A records for you hosts, define the DNS server in your hosts and the vCenter Server then add your hosts using their fully qualified name. Any tasks that perform operations like adding hosts, require the client machine running the vSphere Client to be able to resolve the host names. These tasks will fail even if the vCenter Server can resolve the fully qualified host name.
Therefore if the client machine can’t resolve the hosts, remotely login to the vCenter Server to perform the tasks. Then once the hosts are added you can switch back the client machine. A host file won’t help and the only other alternative is to point your client machine at a DNS server that can resolve the fully qualified name for the hosts.