[CLUE-Tech] Migrating to different server

[Todd A. Gibson]

G'day!

Question first:  Do you have any tips or tricks for migrating
from one production server to another?

Background: I'm running my own server exposed to the internet via
DSL/NAT.  Among other things, it is doing the following:
* DHCPD and DNS for my LAN
* Apache Web server for a half-dozen domains.
* Mail gateway for incoming and outgoing mail for same domains
  (via Sendmail, FWIW)

I just received a new rackmount server (with a cooling fan that makes my
ears bleed, but that's another story).  I want to migrate from my
current server to the rackmount server.

I am not in a hurry to migrate, but when all is ready, I want to switch
over with no more than 1-2 hours of downtime so-as the users don't
scream and I don't panic.

I've done some initial configuration of the new server, but now, not
having switched production servers before, I find myself hemming and
hawing on how to proceed.  Examples of what does/doesn't perplex me:

* Some Web applications use a database and/or a vast collection of
obscure Perl modules.  I think I know how to proceed here.  Prior to
switching, I can put a copy of the Web apps on the new server, and start
tinkering with the DB and Perl installation until the new apps are
running smoothly.

* DHCPD and DNS.  Since this only impacts my LAN, I believe I can leave
this on the old server and switch it over on a schedule independent of
migrating everything else.  Yes?

* Mail.  This troubles me.  I'm afraid of switching over and then
encountering problems which means incoming mail bounces while I figure
out the problem.  Is the solution here to find someone willing to 
be a secondary mail host, add an MX record, and then have at it?  Or is
it OK to make my new server a secondary mail host, switch over, then
make the new server primary?  Also, I don't know how to test any mail
functionality on the new box other than running it in production.

* Web configuration.  I think I can start with my current configuration
file, taking care of any paths that need to change, and then I'm fine.

* Users.  There are several user accounts on the production box.  To
copy the home directories over is trivial, but what about the actual
accounts?  Somehow, just copying entries from /etc/passwd (and
/etc/shadow?) doesn't seem right.

* Finally, I imagine I would have to build a data transition plan that
I practiced before switching.  For example, exporting the databases
on the old box and importing them into the new box.

I know the topic merits several chapters in a book, if not an entire
book in and of itself.  Short of writing that book for me, does anyone
have any suggestions, tips, or tricks that might ease this first-timer's
production box switch?

Thanks,
-TAG