Since you are Gentoo user, i don’t need to go to details. You know what you doing.

Update: Mod-rails now works with apache mpm-worker

1. Recompile Apache non-threaded

add this to /etc/portage/package.use

www-servers/apache -threads

and this to /etc/make.conf

APACHE2_MPMS="prefork"

2. Re emerge apache

# emerge -va apache

3. Passenger is in gentoo portage, but its in testing. Currently Version 2.0.1

# echo "www-apache/passenger" >> /etc/portage/package.keywords

4. Install Passenger

# emerge -va passenger

If it tries to install rails 2.2.2, rake, and lots of other gems that you already have installed trough rubygems, then run emerge with –nodeps option

# emerge -va --nodeps passenger

5. Edit /etc/conf.d/apache and add “-D PASSENGER” to apache options

for example mine looks like this:

APACHE2_OPTS="-D DEFAULT_VHOST -D INFO -D LANGUAGE -D PROXY -D PASSENGER"

That’s it.

Now just drop a similar vhost config file inside /etc/apache/vhosts.d/

This is a sample vhost file for a rails app.

<VirtualHost *:80>
  ServerName mydomain.com
  DocumentRoot /myapp/public
  Include /etc/apache2/vhosts.d/deflate.conf
  RailsBaseURI /
  # The maximum number of Ruby on Rails application instances that may be simultaneously active.
  # A larger number results in higher memory usage, but improved ability to handle concurrent HTTP clients.
  # normally 1 to 10. (1 for each 50mb ram)
  RailsMaxPoolSize 1
  # The maximum number of seconds that a Ruby on Rails application instance may be idle.
  # That is, if an application instance hasn't done anything after the given number of seconds,
  # then it will be shutdown in order to conserve memory. ( 1 hour)
  RailsPoolIdleTime 3600
  RailsEnv 'production'
  <Directory /myapp/public>
    Options FollowSymLinks
    AllowOverride None
    Order allow,deny
    Allow from all
    </Directory>
</VirtualHost>

My sample deflate.conf,
used to gzip the content

<Location />
	SetOutputFilter DEFLATE
	#
	# Netscape 4.x has some problems...
	BrowserMatch ^Mozilla/4 gzip-only-text/html
	#
	# Netscape 4.06-4.08 have some more problems
	BrowserMatch ^Mozilla/4\.0[678] no-gzip
	#
	# MSIE masquerades as Netscape, but it is fine
	BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
	# NOTE: Due to a bug in mod_setenvif up to Apache 2.0.48
	# the above regex won't work. You can use the following
	# workaround to get the desired effect:
	BrowserMatch \bMSI[E] !no-gzip !gzip-only-text/html
	# Don't compress images
	SetEnvIfNoCase Request_URI \.(?:gif|jpe?g|png)$ no-gzip dont-vary
	SetEnvIfNoCase Request_URI \.(?:exe|t?gz|zip|bz2|sit|rar)$ no-gzip dont-vary
	SetEnvIfNoCase Request_URI \.pdf$ no-gzip dont-vary
	# Make sure proxies don't deliver the wrong content
	Header append Vary User-Agent env=!dont-vary
</Location>

DeflateFilterNote Input instream
DeflateFilterNote Output outstream
DeflateFilterNote Ratio ratio
LogFormat '"%r" %{output_info}n/%{input_info}n (%{ratio_info}n%%)' deflate
CustomLog /var/log/apache2/deflate_log deflate

* Update on July 10, 2008.

- Now using gentoo portage to install it. it’s more smooth.

Note:

Personally I found that Thin + nginx uses less memory(Nginx 4MB + each thin server) than
apache + passenger, which uses quite more. (Apache: 50MB + each rails spawner)