在活动目录中部署两台主控域控制器，两台域控制器互为冗余。
Server 2012 R2新建活动目录和DC
refer to： https://www.cnblogs.com/jfzhu/p/4006118.html
Add another domain controller as backup domain controller.
1. Create vm and rename computer name
2. Close firewall
3. Add existed DC ip as DNS of the backup DC
3. Join this machine to existed domain
4. Install Domain Controller service
Open server manager and click add roles and features
select Role-based or feature-based installation
Click next
select Active Directory Domain Services
Install feature
4. Promote server to a domain controller
select add a domain controller to an existing domain
5. Check two domain controller DNS manager and add two domain controller ip and FQDN for different option
check zone replication scope
add other domain controller ip in name server record of domain properties
add another domain controller ip in zone transfers
check and change the backup dc dns manger
Open Active Directory Users and Computers, we can find all the computers existed dc in backup domain controller