Weird problem with Rails app and Mongrel - ruby-on-rails

Question

I originally posted a question relating to this problem on serverfault.com: https://serverfault.com/questions/152587/apache-mod-proxy-to-another-server
I have since realized that this is not an issue with my server setup, but my rails application. I have set this application up server-wise the exact same as another functioning rails app I have running on the same server. When I start the server my mongrel.log looks like this:
** Daemonized, any open files are closed. Look at /var/www/osuwebdev/tmp/pids/mongrel.pid and log/mongrel.log for info.
** Starting Mongrel listening at 0.0.0.0:8080
** Starting Rails with production environment...
** Rails loaded.
** Loading any Rails specific GemPlugins
** Signals ready. TERM => stop. USR2 => restart. INT => stop (no restart).
** Rails signals registered. HUP => reload (without restart). It might not work well.
** Mongrel 1.1.5 available at 0.0.0.0:8080
** Writing PID file to /var/www/osuwebdev/tmp/pids/mongrel.pid
When I load a page this pops up in the log:
Wed Jun 30 19:46:10 +0000 2010: Error calling Dispatcher.dispatch #<NoMethodError: undefined method `[]' for nil:NilClass>
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel/cgi.rb:108:in `send_cookies'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel/cgi.rb:136:in `out'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel/http_response.rb:65:in `start'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel/cgi.rb:135:in `out'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel/rails.rb:81:in `process'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel.rb:159:in `process_client'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel.rb:158:in `each'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel.rb:158:in `process_client'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel.rb:285:in `run'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel.rb:285:in `initialize'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel.rb:285:in `new'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel.rb:285:in `run'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel.rb:268:in `initialize'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel.rb:268:in `new'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel.rb:268:in `run'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel/configurator.rb:282:in `run'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel/configurator.rb:281:in `each'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel/configurator.rb:281:in `run'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/mongrel_rails:128:in `run'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/../lib/mongrel/command.rb:212:in `run'
/var/lib/gems/1.8/gems/mongrel-1.1.5/bin/mongrel_rails:281
/usr/local/bin/mongrel_rails:19:in `load'
/usr/local/bin/mongrel_rails:19
I cannot figure out what is different about this app that may cause this issue.

Answer 1

I believe this is a weird combination of bugs in Rack, Mongrel, and Rails.
Save this ruby code in your app to config/mongrel.rb: http://gist.github.com/471663
In your config/environment.rb, at the very end of the file add:
require File.join(File.dirname(File.expand_path(FILE)), 'mongrel')
In that same file add this line in the Rails::initializer.run block:
config.gem "mongrel"
Longer explanation of the problem here: https://rails.lighthouseapp.com/projects/8994/tickets/4690-mongrel-doesnt-work-with-rails-238
This has definitely worked for a Rails 2.3.8 app, though I patched it slightly differently than described above.

Answer 2

Do you still see the problem on subsequent GET requests? I had a similar problem where my Rails app would run fine under WEBrick but not under Mongrel but found somewhere on the internets (here's a link that shows a similar version of the problem) that older versions of Mongrel mishandle the first request to the page but handle subsequent requests ok.
The workaround we put in was that whenever we started the app, we'd have curl perform a GET on the app to 'prime' Mongrel.

Answer 3

This is usually a fail reading a yaml file for config. It has set up a config object to get values from and the entry in the yaml file for your environment isn't there so the object is nil.
Are you running any gems that have a yaml file that maybe isn't set up for development?
I don't know why going back to 2.3.5 would help - it might be that it loads things in a different order and the config information is available.