Does anyone know of a good guide for migrating from one Ubuntu server to another.

I am going to move the home of my live ruby on rails application and I need to have as little down time as possible, move all the databases and my postfix/smtp etc. I'd like to be aware of the pitfalls before setting out and a good hand-holding guide would be handy as this is my first time doing this on a live production server.


This is not a duplicate of best practice to migrate server

My question: Does anyone know of a good guide?

I mean a tutorial, not a simple list of some pointers but a step by step guide.

The linked question: A handful of things to consider.

Very much not a duplicate. I asked this on stackoverflow and server fault, it is outside the scope of those pages, however, there are much better answers on those networks already to the light list of things to consider. What I'm looking for is a guide or tutorial.