1. Install mod_fcgid. On Debian-derived systems,
   "sudo apt-get install libapache2-mod-fcgid"
   To install from the source and to learn more,
   http://httpd.apache.org/mod_fcgid/

2. Choose a directory for the Yesod application that will
   run as fcgi. I my example, I will use /usr/local/YBother.
   The name of the app binary will be "YBother" too.

3. In your Apache configuration, create a section for the
   YBother app running under FastCGI:

   <IfModule mod_fcgid.c>
   <Location /YBother> # Use "/" if the whole VirtualHost is the app
   	Options ExecCGI
   	Order allow,deny
   	allow from all
   	SetHandler fcgid-script
   	FcgidWrapper "/usr/local/YBother/YBother Production" virtual
   </Location>
   </IfModule>

   It is important to specify the flag 'virtual'
   in the FcgidWrapper directive.

4. Install the package wai-handler-fastcgi via cabal install.
   Add the 'build-depends' dependency to your .cabal file:

       , wai-handler-fastcgi           >= 1.1        && < 1.2

5. *** WORKAROUND *** WORKAROUND *** WORKAROUND ***

   Before proceeding, we must make a workaround for a
   problem that exists as of mod_fcgid 2.3.6 and
   wai-extra 1.1.0. The nature of the problem is this:
   when run in 'virtual' mode, mod_fcgid does not set
   PATH_INFO variable (and neither PATH_TRANSLATED),
   presumably because the logic of the implementation
   of 'virtual' makes it think that any path in the URL
   is the path of the ("virtual") handler binary itself.
   Still, it does set the variable SCRIPT_NAME to exactly
   what the application would like to see as the value
   of PATH_INFO.

   Now, I could argue that mod_fcgid *should* set
   PATH_INFO equal to SCRIPT_NAME and PATH_TRANSLATED
   equal to SCRIPT_FILENAME when the handler is run
   in "virtual" mode because intuitively this seems
   like the Right Thing (tm), and I've filed a bug
   https://issues.apache.org/bugzilla/show_bug.cgi?id=52710
   For now, it is technicaly easier to provide a
   workaround in the WAI CGI module. Specifically, let us
   make it take the value of SCRIPT_NAME if PATH_INFO was
   not present in the request. This is the diff:

index 2d9fb47..14ea6b2 100755
--- a/wai-extra/Network/Wai/Handler/CGI.hs
+++ b/wai-extra/Network/Wai/Handler/CGI.hs
@@ -73,7 +73,13 @@ runGeneric
      -> IO ()
 runGeneric vars inputH outputH xsendfile app = do
     let rmethod = B.pack $ lookup' "REQUEST_METHOD" vars
-        pinfo = lookup' "PATH_INFO" vars
+        pinfo =
+            case lookup "PATH_INFO" vars of
+                Just x -> x
+                Nothing ->
+                    case lookup "SCRIPT_NAME" vars of
+                        Just x -> x
+                        Nothing -> ""
         qstring = lookup' "QUERY_STRING" vars
         servername = lookup' "SERVER_NAME" vars
         serverport = safeRead 80 $ lookup' "SERVER_PORT" vars

   Build and install wai-extra package with this diff applied.

   *** END OF UGLY WORKAROUND ***

6. Change the "main.hs" of your Yesod app to look like this:

import Prelude              (IO)
import Network.Wai.Handler.FastCGI (run)
import Yesod.Default.Config (fromArgs)
import Yesod.Logger         (defaultProductionLogger)
import Settings             (parseExtra)
import Application          (getApplication)

main :: IO ()
main = do
  appconfig <- fromArgs parseExtra
  logger <- defaultProductionLogger
  application <- getApplication appconfig logger
  run application

7. Build the application, and place the binary *AND*
   the directories "config" and "static" with all their
   content into the directory from which Apache will
   execute the handler. Let me stress it: the executable
   must be in the same directory with the "config" and
   "static" subdirectories. This is because when Apache
   starts the executable, it sets the current working
   directory to the executable's `dirname`.

8. Make the "static/tmp" directory writable to the
   httpd process. On Debian-derived systems,

   chgrp -R www-data /usr/local/YBother/static/tmp
   chmod -R g+w /usr/local/YBother/static/tmp

9. Remember to set "approot" to the correct place, e.g.

Production:
  approot: "http://www.example.com/YBother"
  <<: *defaults

10.Restart Apache to make it notice the change of
   configuration.

11.Point your browser to the app root

      http://www.example.com/YBother/

   and verify that things work as expected.