virtualisation vs ltsp chroots

[Gavin McCullagh]

Hi,

On Fri, 15 Feb 2008, David Van Assche wrote:

> I've been told that using a virtualised setup is better than using
> chroots for setting up low fat clients. I have my doubts about this, which
> are really questions I suppose. 

It's an interesting thought.  It sounds a bit overkill to me in most
situations but I guess I can think of some possible benefits.  It also
seems like it would add a lot of complexity to ltsp to have to package up
virtualisation as part of it and make sure that worked.

> For one, I'd imagine that virtualising the chroots will be slower than
> using a chrooted environment, 

Almost certainly.  It certainly won't be quicker :-)

> and that mounting of disks and network points would be more complicated

Not sure about this.  One small issue I've found with extending the chroot
is that if you install openssh-server, it complains that it can't start
(and continues trying to reconfigure itself every time you run apt).  On a
virtualised machine, ssh would be able to start as a full separate tcp
stack should be available so tcp port 22 would not be in use by the
server's ssh instance.  

I'm not sure if there are many more of these sorts of conflicts as I
haven't install much in the chroot.  I'm also pretty sure a careful look at
the dpkg/debconf mailing lists would allow me to get past it.

Depending on the sort of virtualisation used you could perhaps have a
PowerPC virtualised machine running on your server, which would allow you
to manage the PowerPC chroot on the server.  You can't do that in a regular
chroot on an x86 machine.

I guess the virtualised environment needs to either run with the chroot as
it's root fs or more likely on an image which you can then convert to an
LTSP5 root image.  

A possible alternative would be to boot a single "admin" thin client with
nfs and write access to the chroot.  That should allow you to run apt, etc.
It would be dependant on the speed of the thin client though.

Gavin