It's really something that is specific to what we do and I had/have no intention of making it generic or let alone designing the type of thing that helps people who don't have experience doing sys admin - because I want to stay focused. For those that are interested these are the main techniques I use:

First I go to slicehost and create a machine, they send me a email when it's done (about 5 mins or so).

I have one install script and a syncing script, The install scripts one calls the sync script. After the machine is live I just use the sync one to update it. $hostname is the name or IP address of the new machine.

First I copy SSH authorization over, so I can login without a password (assumes you have created SSH keys already - which is one time event):

ssh root@$hostname "mkdir /root/.ssh; echo \"`cat /root/.ssh/id_dsa.pub`\" > /root/.ssh/authorized_keys2"

Then run various commands on the new machine. I put these in a file "commands.fragment". which contains things like

  mkdir /var/www

  groupadd -g600 web

  chgrp web /var/www

  yum -y install iptables ntp

and so on, then run it:

  cat commands.fragment | ssh root@$hostname

The I run the syncing script (which I'll rerun over the life of the machine) Then I sync my code across:

  rsync -avz -e ssh /var/www/ root@$hostname:/var/www/

and programs I've complied:

  rsync -avz -e ssh /usr/local/ root@$hostname:/usr/local/

and so on.

Now we have everything in place we can start the services for whatever the box does, for example to start a web server:

  ssh root@$hostname "/sbin/chkconfig --add lighttpd; /etc/init.d/lighttpd start"

And that's it.

My script took me a few hours to write and I did so that I can scale up (and down) in a hurry by adding a machine rather than taking the existing machines (there are 2) down whilst slicehost resize it - which is not something I wanted do while there is a lot of traffic coming in. We don't really need multiple machines, but buying one big slice is expensive to have running the whole time.

Hope that helps.

Thanks for the excellent follow up! It sure helps.