Source: VMware KB
I was in the process of rebuilding my virtual lab, while setting up vCenter appliance 5.5 I got above error, that not able to connect to active directory. As I knew we can reconfigure this option later, I proceeded with rest of the setup and decided to troubleshoot it later and removed check box from active directory using back button.
Everything got configured correctly except AD authentication, as I have habit to document everything and already created seme on installing and configuring vcenter appliance 5.5. After comparison I found what mistake I did (missed one step) while configuring vcenter appliance which can be seen here. I didn’t provided FQDN. Which was not allowing me to enabling active directory and it was failing.
To change host name I puttied into vcenter appliance and used below commands to verify and correct it.
echo vc001.vcloud.lab > /etc/HOSTNAME
Then verified it using commands that I able to see FQDN correctly.
I also made DNS entries (forward and reverse) for vCenter appliance (Best practices link)
Then checked name resolution from appliance itself.
Restarted appliance to reflect changes. And confirmed that Hostname is showing correctly.
And in the last, reconfiguration AD authentication was successful (under reconfigure vcenter server\Authentication)
Restart appliance one more time to take effect for changes made to AD configuration,
After all this done When I tried to login with vmware vsphere web client. I faced another issue
Failed to connect to VMware Lookup Service https://vc001.vcloud.lab:7444/lookupservice/sdk - SSL certificate verification failed.
For this I enabled certificate regeneration under admin tab and submitted it.
One more restart require for this. And after I am able to login successfully through VMware web client.