How do big web sites roll out new versions?
SingAlong: Well, when Google App Engine comes into play, this problem isn't big. They have something called versioning (in the admin panel) which allows you to change the app to the next version or revert back to an old version.From an amateur POV:
But when usual servers come into play, I have had no clue abt big ones.Infact a couple of months back, when my home server had a burst of traffic from my mobile app, it couldn't handle it (256kbps connection, 256MB ram with a 1.3 GHz P3 processor. well suited to serve a high bandwidth mobile app of 1000 users and also for constantly collecting data from APIs). But due to sudden traffic outburst, I had to string a friend's comp to mine.My procedure: I first stopped updating data from APIs to my DB and kept it static. No updating the DB. Copied it to my friend's fast comp. I had my computer interfaced with a mobile which accepts input from the user mobile phones. That was the app's requirement. So I had an advantage of  lining up requests right there in the mobile phone while I was switching the server. That trick should help if you are developing a mobile app on a very limited resource (a hobby project).