FOSDEM lightning talk
Sunday 2nd Feb 2014, 16:00, H.2215 Ferrer
https://fosdem.org/2014/schedule/event/libguestfs/

Advanced disk image management with libguestfs
libguestfs, virt-builder, virt-sparsify, virt-sysprep

----------------------------------------------------------------------


Good afternoon.  Today I'm going to talk about libguestfs
with is a suite of tools for looking inside and modifying
virtual machine disk images.


virt-builder
------------

First off, a new tool that we've written to create virtual machines.

[ Show the builder.sh script ]
[ Run the builder.sh script ]

I'll come back to this script at the end of the talk.

virt-builder can:

 - output raw, qcow2 and other formats
 - resize using [virt-resize]
 - write a random seed
 - set a hostname
 - edit configuration files
 - install packages
 - run custom scripts
     * at build time
     * or at first boot

Libguestfs can safely and securely inspect and modify disk
images without needing root.

Virt-builder doesn't install guests from scratch.  Instead it
takes clean, cryptographically signed, compressed templates and uses
libguestfs to customize them.



Preparing the templates
-----------------------

virt-builder comes with a handful of templates.

You can also prepare your own.  

Over the years we have come up with a good way
to prepare and distribute reasonably small templates

    virt-install     (or Oz)
        v
    virt-sysprep
        v
    virt-sparsify
        v
       xz

virt-install runs a regular OS install, using anaconda,
debian-installer, etc.  You can automate this completely
using kickstart or preseed.

virt-sysprep unconfigures the guest.  Using libguestfs it
removes SSH host keys, log files, network configuration,
user accounts and so on.

virt-sparsify
-------------

virt-sparsify uses libguestfs to make guests sparse a.k.a.
thin-provisioned.

It looks for unused space:

 - in filesystems

 - in LVM physical volumes

 - swap partitions

Including non-zeroed, but unused blocks.

It converts that to sparseness in the host file.


xz
--

Finally xz compresses the template.  We like xz for several reasons:

 - nearly best in class compression

 - preserves sparseness

 - compressed files can be random accessed  [nbdkit]

 - virt-builder includes parallel uncompress


Results
-------

               disk apparent final
CirrOS 0.3.1     39       18    11 MB
Debian 7       4096      719   142 MB
Fedora 20      6144      826   174 MB
Ubuntu 13.10   4096     1019   187 MB


[At the end of the talk, show the progress of the builder script.]


* libguestfs resources and other tools