Beyond Buildworld Dev Summit Working Group Report

[Tim Kientzle]

On Jun 10, 2013, at 10:02 PM, Glen Barber wrote:

> On Mon, Jun 10, 2013 at 09:25:39PM -0700, Tim Kientzle wrote:
>>> 	• Crochet with VM images [TimKeintzle], [GlenBarber], [ColinPercival]
>> 
>> Per Colin, there's no way for "mere mortals" to upload machine
>> images to Amazon, so there's little point in pursuing that.
>> 
>> I did recently add support to Crochet for building VMWare VM images
>> directly.  Works pretty well; I've been using it to build throw-away
>> images for testing.  This goes a step further than what Glen
>> has recently announced; so far, he's just building the VMDK disk
>> image, Crochet fills in the rest of the VM configuration files.
>> 
>> It should be routine to duplicate the approach to support other
>> VM environments (e.g., Parallels, VirtualBox, OFA).  My time is
>> limited but I'm happy to assist if someone else wants to work on it.
>> 
> 
> I do intend to look at how Crochet does this, because I think your
> implementation is far more user friendly and cross-application
> compatible.
> 
> I'll certainly pick your brain on it, if you don't mind. 

Key point:  VM images are directories which contain
a number of different files.  The disk image is just one
of those.  For VMWare (and others I've looked at), the
VM directory contains:

* Disk image - this can be a straight disk image (which
   is what Crochet currently uses) or a
   structured/sparse/compressed "virtual disk"
 
* Disk descriptor -- this specifies the format of the disk
   image and the parameters of the virtual disk drive.

* VM descriptor -- this describes the rest of the virtual
   hardware.

VMWare seems to be the simplest of the ones I've
looked at:  the descriptor files are lists of key/value pairs
and the VMWare software can boot a VM even from
a pretty skeletal definition.  It didn't take me very many
tries to get Crochet to build a VMWare image that
VMWare Fusion was comfortable booting.  It helps
that the VMWare file formats are pretty well documented:
In particular:  http://sanbarrow.com

Parallels and OFA both use more complex XML configuration
files -- everything has an ID and there are lots of cross-references.
I've toyed with building Parallels VMs but haven't gotten
very far yet.

qemu-img seems like a nice tool for generating a virtual disk image,
but it doesn't currently know how to create compressed
VMWare disks.  I've skimmed VMWare's documentation and
it doesn't look too hard to build a compressed VMWare disk
if someone would like to tackle that.  ;-)

Tim

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