The Manager Service is a Windows service that coordinates communication between IaaS Distributed Execution Managers, the database, agents, proxy agents, and SMTP.
Your IaaS deployment requires that only one Windows machine actively run the Manager Service. For backup or high availability, you may deploy additional Windows machines where you manually start the Manager Service if the active service stops.
Simultaneously running an active Manager Service on multiple IaaS Windows servers makes vRealize Automation unusable.
The Manager Service communicates with the IaaS Web site through the Model Manager and must be run under a domain account with administrator privileges on all IaaS Windows machines.