System update spec proposal

[Christopher Blizzard]

A few notes follow here.

First about approach: you should have given this feedback earlier rather
than later since Alex has been off working on an implementation and if
you're not giving feedback early then you're wasting Alex's time.  Also
I would have appreciated it if you had given direct feedback to Alex
instead of just dropping your own proposal from space.  It's a crappy
thing to do.

So notes on the proposal:

1. There's a lot in here about vserver + updates and all of that is
fine.  But we've been pretty careful in our proposals to point out that
how you get to the bits to the box is different than how they are
applied.  I don't see anything in here around vserver that couldn't use
alex's system instead of rsync.  So there's no added value there.

2. rsync is a huge hammer in this case.  In fact, I think it's too much
of a hammer.  We've used it in the past ourselves for these image update
systems over the last few years (see also: stateless linux) and it
always made things pretty hard.  Because you have to use lots random
exceptions during its execution and once it starts you can't really
control what it does.  It's good for moving live image to live image,
but I wouldn't really want to use it for an image update system -
especially one that will be as distributed as this.  Simply put I see
rsync as more of a tool for sysadmins than for a task like this.  I
think that we need something that's actually designed to solve the
problems at hand rather than seeing the hammer we have on the shelf and
thinking that it's obviously the right solution.

3. It doesn't really solve the scaling + bandwith problems in the same
way as Alex's tool does.  Still requires a server and doesn't let you
propagate changes out to servers as easily as his code does.

Basically aside from the vserver bits, which no one has seen, I don't
see a particular advantage to using rsync.  In fact, I see serious
downsides since it misses some of the key critical advantages of using
our own tool not the least of which is that we can make our tool do what
we want and with rsync you're talking about changing the protocols.

Anyway, I'll let Alex respond with more technical points if he chooses
to.

--Chris