The IaaS Manager Service and Distributed Execution Management (DEM) server of vRealize Automation handle the business logic, and maintain the workflows for provisioning and lifecycle management of virtual machines. Consider the number of instances according to the design objectives and the sizing for these components.

The IaaS Manager Service оf vRealize Automation has the following functions:

  • Manages the integration of vRealize Automation IaaS with external systems and databases.

  • Provides business logic to the DEMs.

  • Manages business logic and execution policies.

  • Maintains all workflows and their supporting constructs.

A Distributed Execution Manager runs the business logic of custom models by interacting with another vRealize Automation instance (repository) as required.

Each DEM instance acts in either an orchestrator role or a worker role. The DEM Orchestrator monitors the status of the DEM Workers. If a DEM Worker stops or loses the connection to the Model Manager or repository, the DEM Orchestrator puts the workflow back in the queue.

The DEM Orchestrator performs the following operations:

  • Manages the scheduled workflows by creating workflow instances at the scheduled time

  • Allows only one instance of a particular scheduled workflow to run at a given time.

  • Pre-processes workflows before execution. Preprocessing includes checking preconditions for workflows and creating the execution history of the workflow.


The vRealize Automation IaaS Manager Service and DEM Orchestrator are separate services, but you install them on the same virtual machine.

Table 1. Resource Requirements for the IaaS Model Manager and DEM Orchestrator Server of vRealize Automation per Virtual Machine






8 GB



Local drives


vRealize Automation functions

IaaS Manager Service, DEM Orchestrator

Operating system

Microsoft Windows Server 2012 SP2 R2

Table 2. Design Decisions on vRealize Automation IaaS Model Manager and DEM Orchestrator Server

Decision ID

Design Decision

Design Justification

Design Implication


Deploy two virtual machines to run both the vRealize Automation IaaS Manager Service and the DEM Orchestrator services in a load-balanced pool.

The DEM Orchestrator must have strong network connectivity to the Model Manager at all the time.

You must provide more resources for these two virtual machines to accommodate the load of the two applications. If additional resources are required in the future, you can scale up these virtual machines later.