[Kimchi-devel] [RFC] Guest cloning

[Brent Baude]

At one point Adam had really suggested we look at how guests are defined
and changed.  In particular, straight copies of XML and or straight
edits of XML could lead (after time) to the XML digressing into
something libvirt might not understand at some point.  

To prevent this sort of problem, we thought that each time a guest is
edited, the XML is created entirely anew but of course using the same
values.  This has the distinct advantage of making future additions of
options easier to integrate.  It is also the exact basis I think would
be appropriate for any sort of cloning and dovetails nicely into your
proposal.  About a month ago I had a working version of this in draft
form.

Would anyone be interested in reviewing it and or adding to it prior to
implementing the clone function?  If so, ping me on IRC and I'll get you
a copy of the patch.

Brent



On Thu, 2014-10-02 at 15:05 -0300, Crístian Viana wrote:
> Hi everyone,
> 
> I'm presenting here my proposal for the feature "Guest cloning" which
> is expected to be implemented for Kimchi 1.4. 
> Description
> Cloning a guest means creating a new guest with a copy of the settings
> and data of the original guest. All data described by its XML will be
> copied completely, with the following exceptions: 
>       * name: the new guest will have an automatically generated name.
>         We can append "-clone<n>" to the original guest's name, where
>         <n> is related to the number of clones created from that
>         guest. For example, cloning a guest named "myfedora" will
>         create a new guest named "myfedora-clone1"; if another clone
>         for that same guest is requested, it will be named
>         "myfedora-clone2". 
>       * uuid: the new guest will have an automatically generated UUID.
>         We can create a random UUID for every cloned guest. 
>       * devices/interface/mac: the new guest will have an
>         automatically generated MAC address for every network
>         interface. We can create random MAC addresses for every cloned
>         guest. 
>       * devices/disk: the new guest will have copies of the original
>         guest's disks. Depending on the storage pool type of each
>         disk, a different procedure may be used to copy that disk: 
>               * DIR, NFS, Logical: the disk file will be copied to a
>                 new file with a modified name (e.g. "disk.img" ->
>                 "disk-clone1.img") on the same storage pool. 
>               * SCSI, iSCSI: the volume data will be copied as a new
>                 disk file on the storage pool "default". 
> REST API
> Only one new REST command will be added. 
> Syntax
> POST /vms/<vm-name>/clone 
> Parameters:
> None. 
> Return:
> An asynchronous Task with "target_uri" containing
> "/vms/<new-vm-name>".
> As expected with any Task, the cloning process can be tracked by
> checking the corresponding task's status. 
> Discussion
> I think the most challenging part of this feature is how to deal with
> different types of disks while not prompting the user with any input.
> There are a lot of possibilities and a lot of things that can go wrong
> during the disks copy but we still need to do whatever is easier for
> the user.  For example, do we really have to create the new disks in
> the same storage pool as the original disk's? If that's not possible
> (e.g. not available space), should we create them in another pool with
> available space? Should we ask any input from the user (e.g. "Would
> you
> like to create the new disk on the same storage pool or on a different
> one?")? What about the *SCSI pool types, is it OK to copy the volume
> data to a different storage pool (i.e. "default") like I'm proposing
> here? I couldn't think of a way to add a new volume in an existing
> pool
> of those types. How about making the *SCSI volumes shareable between
> the original and the new VMs? I don't like that approach because then
> both VMs will use the same disk, whatever is changed in one VM is also
> changed in the other one, and that's not a clone for me, that's a
> "hardlink".
> 
> Any feedback is welcome!
> 
> Best regards,
> Crístian. 
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