Re: migration and installation 50 THOUSAND machines
I would suggest using most of the ideas outlined in
http://infrastructures.org/ - though the text on the website is a bit
dated, you can manage a large infrastructure of 50K systems combining
the conceptual framework laid out by Steve Traugott, with Debian tools
and modern configuration tools (cfengine, puppet). Having said that, I
am still deeply impressed by the simple approach of using makefiles
that drives the originall version of IsConf.
An intriguing project that might be "the missing piece" is IsiSetup -
http://www.isisetup.ch/ - but haven't had the time to review it or use
it. If it does what it promises - integration with apt/dpkg to store
config files of debian packages in a git repo to allow management of
machine configuration as an extension of the apt/dpkg infrastrucuture,
it could be a killer app.