multi site with lighttpd

include_shell just calls the shell script to generate the config, so it'll only be called once when lighttpd is started up.

[Citation needed.] Are you sure about that? I haven't found anything supporting that in Lighty's docs - but then again, I haven't found anything supporting that it'll run once for each hit either.

I think you may have some misunderstandings of how mod_simple_vhost works. We are using it to host both a large multi-site Drupal 6 installation as well as a smattering of non-Drupal or Drupal 5-powered sites.

Consider that your web root looks like this:

html-site.xyz
wordpress-site.xyz
drupal-multisite.xyz

What happens if you configure mod_simple_vhost like this:

simple-vhost.server-root = "/path/to/web/root/"
simple-vhost.default-host = "drupal-multisite.xyz"
simple-vhost.document-root = "/"

When Lighty gets a request for any given domain name, it will first check to see if a directory matching that domain name exists in the web root. If so, it will host from that directory; if not, it will host from the simple-vhost.default-host directory. If you want to add another Drupal multisite, just add the directory to Drupal's sites folder as normal and away you go. If you want to add another non-Drupal site, just add a new directory to the web root which matches the new site's domain name and away you go (though Lighty seems to cache which directory it uses for which domain name, so you may need to restart it if it looks like it's still trying to host from the simple-vhost.default-host directory). That is so wonderfully easy! And you don't need a script to add host names based on Drupal's sites directory - it happens automatically.

It doesn't solve your cross-site file problem, no, but that could be taken care of at the Lua layer if you really think it's a problem (it doesn't bother me, personally, because if I never link to a file at a path like that, it effectively doesn't exist). And, no, that in itself won't allow you to use custom config files per host, though it's still possible (if a little painful) to do just in the configuration file, without resorting to anything external:

$HTTP["host"] == "html-site.xyz" {
  # stuff
}
else $HTTP["host"] == "wordpress-site.xyz" {
  # stuff
}
else $HTTP["host"] != "" {
  # default stuff - note that Lighty's config syntax doesn't support "else" by itself
}

…Where the lines in between the curly brackets could be config stuff, include lines if you really must have each site's config stuff in separate files, or both. (Lighty 1.5 will give us a $PHYSICAL["path"] which will probably work a little better for this sort of thing.)

This is all a generalization of how I've been operating my company's Lighty-powered web server in the real world for almost a year now.