It could happen that you needs to change your of one of your domain controllers. Or perhaps a DNS server. You can do this by changing all settings in Horizon DaaS

Once this is done everything seems to work until you reboot both appliances. Then the network devices will be rest of course. And after the reboot the domain is not accessible anymore. And when you look into the desktone log file you will proberbly see something like this:
2020-06-14 18:11:07,529 ERROR [com.desktone.directory.activedirectory.util.ActiveDirectoryLocationOptimizer]-[pool-11-thread-1] Unable to resolve addresses for domain ‘domeinname.local’: domeinname.local
2020-06-14 18:11:07,529 WARN [com.desktone.directory.activedirectory.util.ActiveDirectoryLocationOptimizer]-[pool-11-thread-1] Unable to discover any domain controller addresses to use for domain ‘domeinname.local’
2020-06-14 18:11:07,529 INFO [com.desktone.directory.DirectoryLocationOptimizer]-[pool-11-thread-1] Completed discovery and optimization of domain controllers for all domains
2020-06-14 18:11:07,529 INFO [com.desktone.directory.DirectoryLocationOptimizer]-[pool-11-thread-1] Discovering and optimizing access to service accounts and global catalog servers
2020-06-14 18:11:07,545 ERROR [com.desktone.directory.activedirectory.util.ActiveDirectoryLocationOptimizer]-[pool-10-thread-1] 01.03.21:Unable to resolve domain suffix domeinname.local
2020-06-14 18:11:07,546 ERROR [com.desktone.directory.activedirectory.ActiveDirectoryAccessManager]-[pool-10-thread-1] getDomainMap, failed to get domain map for domeinname due to error: null
com.desktone.directory.exception.InvalidADDomainConfigException: null
at com.desktone.directory.activedirectory.util.ActiveDirectoryLocationOptimizer.getActiveDirectoryURIs(ActiveDirectoryLocationOptimizer.java:401) ~[dt-directory-server-impl-8.0.0.jar:?] [……]
2020-06-14 18:11:07,554 ERROR [com.desktone.directory.activedirectory.ActiveDirectoryAccessManager]-[pool-10-thread-1] Exception caught getting domain users for domeinname
after trying to ping the netbios and fqdn, my first look is the resolv.conf (cat /etc/resolv.conf)

# DO NOT EDIT THIS FILE BY HAND — YOUR CHANGES WILL BE OVERWRITTEN
That message is clear, do not change because it does not work. The resolution in this case is to change the interfaces settings and reboot!
- sudo vi /etc/network/interfaces
- change dns-nameservers
- save
- logon to second appliance and repeat the steps
- reboot both appliances trough the DaaS service portal

After this action you are able to ping the domain again. And logon to the admin portal.
Soon I will try to reproduce this step in DaaS 9 (20.2)
Greate post, thank you.
Could you please explain, how I can register extra AD Domain using Hdaas 9.0 admin portal?
I feel that I need to add extra DNS server,but cant find where.