title: Ubuntu instance in Amazon WS EC2: How to upgrade Ubuntu to the next version, so it will work after restating it?
body: <p><strong>Background</strong>:<br>
  Some time ago I have an instance on Amazon Web Services EC2, loaded with Ubuntu version 10.x. As soon as version 11 came out, I decided to upgrade it. I did, and everything seemed fine. I even restarted Ubuntu itself (just the OS itself, not the instance), and it worked again. But when I stopped and started the instance itself, Ubuntu would not work again ever. </p>
  
  <p><strong>Reason</strong>:<br>
  I imagine the reason: Ubuntu must have had some kind of "interface software" (so to say) to communicate itself with the virtualization software outside. For example, when we restart the whole instance and it gets a new IP address, there must be a way for the virtualization software to communicate with Ubuntu and tell it what is the new IP address so Ubuntu will boot knowing it. So I guess that when we start our instance using a preloaded well known AMI, that AMI contains an Ubuntu installation that already include that interface software inside. So I guess that when I upgraded Ubuntu from 10.x to 11, that software inside was lost.</p>
  
  <p><strong>Question</strong>:<br>
  Is there a way to know how to install again that component/module/package (or whatever the name is) just after I upgraded the instance, so it will work again when I restart the whole instance? I don't want to be forced to create a new Ubuntu instance from scratch, from a new AMI, if I want to upgrade. I would hate to install all my software again.</p>