Re: web server migration

[Avi Greenbury <lists@avi.co>]

steve reilly wrote:

> question.  how would YOU do it with minimal hassle, ie. having to
> edit config files, databases and such.  this thing has been running
> since etch and been a learning process along the way....  i doubt my
> idea of cloning would work, but?

If they're relatively small and static, it's quite hard to get wrong :)
If there's no DNS to change (as it sounds like there wont be) it's even
harder.

Basically, I would:

* Manually install the packages on the new machine. You can use dpkg
  --set-selections and friends, but for just a website you're probably
  looking at <10 packages and here's a good chance to not also install
  everything you used to want on the previous machine.
* Create a database on the new machine and populate it (by dumping out
  of the old one and importing to the new one)
* Tar up the site, scp it across, untar it into the document root on
  the new server.
* Edit your /etc/hosts file to point the domain at the new server,
  poke around the site and check that everything's in order. Fix stuff
  that isn't.
* Do another dump-and-transfer of the SQL (and files if neccesary)
* Switch your router to point incoming web traffic at the new machine
  and not the old one.

If you've a DNS change to make, then you need to bear in mind that
during the propagation time (which is always at least 30 minutes)
visitors could hit either site (and, therefore, DB). I'd, then, point
the old site at the new DB. You still may need to manage traffic
writing to the db while your dumping,scping,importing and then changing
config, but not normally on family sites :)

Most of the migrations like this that I do are relatively simple PHP
sites (wordpress, or home made), you may have complications with
Postgres if that's what you've used, though. Perl hardly changes in
Debian and maintains backwards compatibility, so that's fine.

You will go from PHP 5.2.x to 5.3.x in Lenny -> Squeeze, though. that
doesn't break things quite as much as 4.x to 5.x did, but there's a
couple of changes that do break things. I'm not enough of a PHP
developer to know precisely what they are, though, so it's a good idea
to check everything does do what you want it to before migrating it
properly.

-- 
Avi