Thursday, March 14, 2013

Windows Sysprep and VM creation

I've seen a ton of blog posts, reference documents and white papers all instructing you—the virtualization admin—to build "template" VMs in the following fashion:

  1. Create a VM and install the OS
  2. Install standard applications
  3. Set all your configuration settings
  4. Patch & Update the OS and applications
  5. Sysprep
  6. Convert to Template
I'm here to tell you now: stop doing Step 5. Don't sysprep those golden images. At least, don't do it in your template process.

At the very least, using this model means you won't be able to update that template more than 3 times: doing a standard sysprep—without a custom unattended settings file—will "rearm" the software activation only so many times. If you run out of "rearms" you get the joy of rebuilding your golden image.

There is a way around the sysprep limit—see the SkipRearm post for my method—but that still leaves you with a VM template that's going to roll through the remainder of the Sysprep process the first time you turn it on—which you'll be doing every time you want to patch or update the image.

Instead, make Sysprep part of your new VM creation process. With VMware, you can easily convert a VM  back-and-forth from a template to a VM; in fact, for the longest time, I never even converted VMs to templates because there didn't seem to be much value in them: everything you could do to a template, you could do to a VM, while there are things you can do with a VM that you can't do to a template.

Instead, leave your golden image at Step 4; you will be revisiting it every month anyway, right?

Every time you need to spin up a VM from that point forward, you will have a (relatively) recently-patched starting point. In fact, if you're really efficient, you'll run the template VM before creating a new machine from it and patch that machine. Either way, you'll be patching a VM; but if you need to spin up more than one VM, the patching is already complete!

So here's my process:
A) Create your golden image
B) Update your golden image
C) Clone a new VM from the golden image
D) Run Sysprep (with or without SkipRearm and other unattended settings)
E) Repeat steps C-D as needed
F) Repeat step B as needed

Note: I realize there are certain setups that require you to leave a template/golden image at the post-Sysprep shutdown state. In those cases, just make sure you've got a snapshot prior to Sysprep so you can revert to a state before it was ever run.

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