Remotely Disable/Enable site in web farm for maintenance?

[gabedog]

What would be a good (and safe) way to enable/disable a web site in a
web farm that needs to come down for maintenance?

Periodically, we have db folks that run db scripts. I'd like to put a
back door page with a login that would allow me to remotely enable and
disable the site. The site is in a web farm. The site has a previously
posted message to users when the site will go down. How can this be
done safely and efficiently in a web farm using sql server session
state?

The db server doesn't entirely go down, so we can have a separate table
that can store values. I know that there can be dependencies in the
web.config or we can cycle the app domain by adding something to the
directories, but there a sync time question accross the servers, plus
we need to deal with existing users that are logged in... Basically,
once the site it 'down' the user would be redirected to the login.aspx
page where the controls would be disabled. Even if they have existing
session state, they can no longer work (so they don't interfere with
the db scripts) ...they were given prior knowledge anyway
:- )

How do people normally handle this?

Regards,
Gabe.