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Wednesday, 25 February 2015

DEM's vs Agents in vCAC

The original functionality was all based on agents, the agent was installed to do one thing, and it could only do one thing. It connects to the manager service via SOAP, and requires installing a dedicated agent for a particular type of endpoint. The DEM communicates with the web server via REST, it does not maintain a personality like an agent, but pulls down the required workflows at runtime. This allows you to update a given workflow one time centrally, and all the DEM's will run that new version next time they execute it.

There was an architectural decision after the DEM was introduced, that new functionality would be written into the DEM type platform and originally DynamicOps was talking about moving the agent functionality into the DEMs (never happened). So you will see things like Amazon EC2, physical provisioning, calling vRO, etc. are executed by the DEM Workers, but the original core functionality of the product (vSphere, Hyper-V, etc) have associated agents that execute that work.

DEMs are used for provisioning and managing machines on:
1.       VMware® vCloud Director® and VMware vCloud® Hybrid Service™ 
2.       Red Hat Enterprise Virtualization (RHEV) Manager
3.       Microsoft System Center Virtual Machine Manager (SCVMM)
4.       Amazon Web Services
5.       Physical Server Management Interfaces for Dell, HP, and Cisco
Agents are used for provisioning and managing machines and services on:
1.       Hypervisor proxy agents (VMware vSphere®, Citrix, XenServer, Hyper-V)
2.       External provisioning infrastructure (EPI)
3.       Virtual Desktop Infrastructures (VDIs)
4.       Windows Management Instrumentation (WMI)

The DEM can be installed as either a DEM Orchestrator or a DEM Worker. At least one DEM instance must be present for each role.  Additional instances can be added for scalability and availability.
The DEM Orchestrator provides the following functions:
a.       Monitors and manages the DEM Worker status:
                                                   i.      If a DEM Worker fails, the DEM Orchestrator shifts the workflow to another DEM Worker instance.
b.      Schedules workflows
c.       Generates workflow history for reporting

DEM Workers communicate with the external systems to execute workflows.