TurnKey Linux's take on Ubuntu appliance development: KISS

[Soren Hansen]

On Tue, Dec 08, 2009 at 07:07:37AM +0200, Liraz Siri wrote:
> You can preseed debconf configuration variables in a tklpatch as well.
> Unfortunately usually the amount of configurability provided via
> debconf is fairly limited.

That's the thing: We are completely free to extend that as much as we
please. Please, please, do not consider this a limiting factor.

> * interaction between an infinite set of possible starting points and
>   your "appliance"

I would recommend attacking these problems one at a time as they come
up.  Trying to design something that will work for every conceivable use
case is virtually impossible, or at the very least a significant time
sink.

> * how to synchronize appliance development with the development of the
>   underlying distribution. You are doing the work of a system
>   administrator, which usually waits until everything is stable to build
>   production systems out of your distribution.

What we do is develop against the current development release while it's
still in development. That way, if we discover shortcomings, we are
actually completely free to fix them rather than try to work around
them.

> * how to safely update a system-level configuration that may have been
>   changed and tweaked since the user first installed it.

This is not a problem unique to appliances and it's difficult to state a
general solution.

> Our conclusion was that the appliance as a package approach
> unnecessarily complicates all aspects of development. Complicated
> things are hard to understand. They're hard to develop, hard to
> maintain, hard to get right. You pay for complexity with reduced
> productivity, reduced reliability and reduced security.

Reduced security? How so? Can you elaborate?

> Doing it this way cleanly decouples your appliance from any messy
> OS-level / inter-appliance interactions and leverages all of the
> innovation happening in the virtualization industry.

It just so happens that we're in the business of creating an agile,
flexible operating system. We have the luxury of controlling every
single part of the software stack. This gives us many, many levers to
pull and knobs to turn. I don't believe this has been exercised half as
much as it can.

-- 
Soren Hansen                 | 
Lead virtualisation engineer | Ubuntu Server Team
Canonical Ltd.               | http://www.ubuntu.com/
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