How to make an Appilcation that supports ZERO DOWN TIME ?

Jan 7 2011 5:09 AM

I just want to know what are all the techniques or technologies available to make sure that our applications downt time is ZERO.

I mean system should not go down while upgrading, deployment, or any database changes.

Last year I think Google was down for around 2 hours due to some power failures on data centers, that impacts the Internet by 5%.