This is the similar issue I am having upgrading from passenger 3/apache 2.2 to passenger 5/apache 2.4 (the app, puppet dashboard version hasn't changed).
Basically, if you add an 'index.html' file just to check access ok, then it works. But something is restricting 'server index generation'. I have poked this for a 2 days and am now stuck. Got to be something simple!! Your config looks like its mixing apache 2.2 and 2.4 access (Order allow,deny Allow from All is 2.2).
vhost.conf
<IfModule mod_passenger.c>
PassengerRoot /usr/lib/ruby/gems/1.8/gems/passenger-5.0.5
PassengerDefaultRuby /usr/bin/ruby1.8
Listen 3000
<VirtualHost *:3000>
RailsEnv production
RailsBaseURI /usr/share/puppet-dashboard
ServerName dashboard.bob.com
DocumentRoot /usr/share/puppet-dashboard/public
<Directory /usr/share/puppet-dashboard/public/>
PassengerEnabled On
Allow from all
AllowOverride All
Options -MultiViews
Require all granted
</Directory>
ErrorLog /var/log/httpd/dashboard.error.log
LogLevel warn
CustomLog /var/log/httpd/dashboard.access.log combined
ServerSignature On
</VirtualHost>
</IfModule>curl http://127.0.0.1:3000 -vvv
* Rebuilt URL to: http://127.0.0.1:3000/
* Trying 127.0.0.1...
* Connected to 127.0.0.1 (127.0.0.1) port 3000 (#0)
> GET / HTTP/1.1
> User-Agent: curl/7.40.0
> Host: 127.0.0.1:3000
> Accept: */*
>
< HTTP/1.1 403 Forbidden
< Date: Wed, 01 Apr 2015 09:08:40 GMT
< Server: Apache/2.4.12 (Amazon) OpenSSL/1.0.1k-fips PHP/5.5.22 Phusion_Passenger/5.0.5
< Content-Length: 341
< Content-Type: text/html; charset=iso-8859-1
<
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<html><head>
<title>403 Forbidden</title>
</head><body>
<h1>Forbidden</h1>
<p>You don't have permission to access /
on this server.<br />
</p>
<hr>
<address>Apache/2.4.12 (Amazon) OpenSSL/1.0.1k-fips PHP/5.5.22 Phusion_Passenger/5.0.5 Server at 127.0.0.1 Port 3000</address>
</body></html>
* Connection #0 to host 127.0.0.1 left intact....
tail /var/log/httpd/dashboard.error.log
[Wed Apr 01 10:08:40.969847 2015] [autoindex:error] [pid 7765] [client 127.0.0.1:36308] AH01276: Cannot serve directory /usr/share/puppet-dashboard/public/: No matching DirectoryIndex (index.html,index.php) found, and server-generated directory index forbidden by Options directive
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