Clarification of the VM Role

Slalom Consultant Joel Forman

Slalom Consultant Joel Forman specializes in cloud computing and the Windows Azure Platform.

There are a lot of misconceptions about the recently introduced “VM Role” for the Windows Azure Platform.  While a lot of people assume that the VM Role is a venture into the Infrastructure-as-a-Service space, that is not really currently the case.

The VM Role has given developers the ability to create a .vhd file which will be deployed to the Windows Azure platform.   This may make sense when getting a traditional Web or Worker Role into the configured state necessary for your application has proven too difficult or impossible.  Microsoft introduces it as the following…

The VM Role was introduced to make the process of migrating existing Windows Server applications to Windows Azure easier and faster, especially when this involves long, non-scriptable or fragile installation steps. – from Microsoft’s website.

The VM Role still falls under the Platform-as-a-Service offering of the Windows Azure Platform.  You are not being given a virtual machine for you to control and manage.  The VM Role is still ultimately controlled by the Fabric Controller of Azure.  There can be cases that arise where actions would be taken for your VM that are out of your control.  For instance, if you role was considered “unhealthy”, it would be pulled and a new instance of your VM Role would be built in its place, from scratch, from your .vhd image.  Anything that was stored locally on that previous instance would be gone.

Here is one way I like to look at it.  Regardless of what type of Role you use, you are creating and deploying an application package.  Web and Worker Roles have a .cspkg file.  The VM Role’s application package is a .vhd file.

I think application developers building applications on the Azure platform are best advised to target Web and Worker roles first, and use the VM Role for applications that cannot be setup in a Web or Worker role.

– Joel

Follow Joel on Twitter: @seattlejoel.

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About Joel Forman
Joel Forman is a Solution Architect at Slalom Consulting and specializes in cloud computing and the Windows Azure Platform.

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