title: Heroku "at=error code=H10 desc="App crashed" method=GET path=/favicon.ico"
body: <p>I have a simple Rails app that works fine on localhost (Mac OS X), but when I deploy it to Heroku I see a page with this error:</p>
  
  <p><strong>Application Error
  An error occurred in the application and your page could not be served. Please try again in a few moments.
  If you are the application owner, check your logs for details.</strong></p>
  
  <p>I don't really know what I'm doing here; I can't make any sense whatsoever of the output from <code>heroku logs</code>:</p>
  
  <pre><code>2013-04-08T03:25:02+00:00 app[web.1]: =&gt; Booting WEBrick
  2013-04-08T03:25:02+00:00 app[web.1]: =&gt; Rails 3.2.12 application starting in production on http://0.0.0.0:15072
  2013-04-08T03:25:02+00:00 app[web.1]: =&gt; Call with -d to detach
  2013-04-08T03:25:02+00:00 app[web.1]: =&gt; Ctrl-C to shutdown server
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:438:in `each'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:438:in `block in eager_load!'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:436:in `each'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:436:in `eager_load!'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/application/finisher.rb:53:in `block in &lt;module:Finisher&gt;'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:30:in `instance_exec'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/app/controllers/application_controller.rb:1:in `&lt;top (required)&gt;'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:439:in `block (2 levels) in eager_load!'
  2013-04-08T03:25:02+00:00 app[web.1]: /app/app/controllers/application_controller.rb:3:in `&lt;class:ApplicationController&gt;': uninitialized constant ApplicationController::SessionsHelper (NameError)
  2013-04-08T03:25:02+00:00 app[web.1]: Exiting
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:54:in `run_initializers'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/application.rb:136:in `initialize!'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/railtie/configurable.rb:30:in `method_missing'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/config/environment.rb:5:in `&lt;top (required)&gt;'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/config.ru:3:in `require'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:54:in `each'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/config.ru:3:in `block in &lt;main&gt;'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/builder.rb:51:in `initialize'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:30:in `run'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:55:in `block in run_initializers'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/config.ru:in `&lt;main&gt;'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/builder.rb:40:in `eval'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/builder.rb:40:in `parse_file'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/server.rb:200:in `app'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/builder.rb:51:in `instance_eval'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/config.ru:in `new'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands/server.rb:46:in `app'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/server.rb:304:in `wrapped_app'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/server.rb:254:in `start'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands/server.rb:70:in `start'
  2013-04-08T03:25:02+00
  :00 app[web.1]:     from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:50:in `&lt;top (required)&gt;'
  2013-04-08T03:25:02+00:00 app[web.1]:   from script/rails:6:in `require'
  2013-04-08T03:25:02+00:00 app[web.1]:   from script/rails:6:in `&lt;main&gt;'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:55:in `block in &lt;top (required)&gt;'
  2013-04-08T03:25:02+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:50:in `tap'
  2013-04-08T03:25:03+00:00 heroku[web.1]: State changed from crashed to starting
  2013-04-08T03:25:03+00:00 heroku[web.1]: State changed from starting to crashed
  2013-04-08T03:25:03+00:00 heroku[web.1]: Process exited with status 1
  2013-04-08T03:25:05+00:00 heroku[web.1]: Starting process with command `bundle exec rails server -p 7369`
  2013-04-08T03:25:09+00:00 heroku[web.1]: State changed from crashed to starting
  2013-04-08T03:25:09+00:00 app[web.1]: DEPRECATION WARNING: You have Rails 2.3-style plugins in vendor/plugins! Support for these plugins will be removed in Rails 4.0. Move them out and bundle them in your Gemfile, or fold them in to your app as lib/myplugin/* and config/initializers/myplugin.rb. See the release notes for more on this: http://weblog.rubyonrails.org/2012/1/4/rails-3-2-0-rc2-has-been-released. (called from &lt;top (required)&gt; at /app/config/environment.rb:5)
  2013-04-08T03:25:09+00:00 app[web.1]: DEPRECATION WARNING: You have Rails 2.3-style plugins in vendor/plugins! Support for these plugins will be removed in Rails 4.0. Move them out and bundle them in your Gemfile, or fold them in to your app as lib/myplugin/* and config/initializers/myplugin.rb. See the release notes for more on this: http://weblog.rubyonrails.org/2012/1/4/rails-3-2-0-rc2-has-been-released. (called from &lt;top (required)&gt; at /app/config/environment.rb:5)
  2013-04-08T03:25:11+00:00 app[web.1]: Exiting
  2013-04-08T03:25:11+00:00 app[web.1]: /app/app/controllers/application_controller.rb:3:in `&lt;class:ApplicationController&gt;': uninitialized constant ApplicationController::SessionsHelper (NameError)
  2013-04-08T03:25:11+00:00 app[web.1]: =&gt; Ctrl-C to shutdown server
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:439:in `block (2 levels) in eager_load!'
  2013-04-08T03:25:11+00:00 app[web.1]: =&gt; Call with -d to detach
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/app/controllers/application_controller.rb:1:in `&lt;top (required)&gt;'
  2013-04-08T03:25:11+00:00 app[web.1]: =&gt; Booting WEBrick
  2013-04-08T03:25:11+00:00 app[web.1]: =&gt; Rails 3.2.12 application starting in production on http://0.0.0.0:7369
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:436:in `each'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:54:in `each'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:436:in `eager_load!'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:438:in `block in eager_load!'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:30:in `instance_exec'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/application/finisher.rb:53:in `block in &lt;module:Finisher&gt;'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:55:in `block in run_initializers'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/application.rb:136:in `initialize!'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:438:in `each'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/config.ru:in `new'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/builder.rb:51:in `initialize'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:30:in `run'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/railtie/configurable.rb:30:in `method_missing'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/builder.rb:40:in `eval'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/initializable.rb:54:in `run_initializers'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/config/environment.rb:5:in `&lt;top (required)&gt;'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/config.ru:3:in `require'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/config.ru:3:in `block in &lt;main&gt;'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/builder.rb:51:in `instance_eval'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands/server.rb:46:in `app'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/server.rb:254:in `start'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/config.ru:in `&lt;main&gt;'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/builder.rb:40:in `parse_file'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/server.rb:200:in `app'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/server.rb:304:in `wrapped_app'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands/server.rb:70:in `start'
  2013-04-08T03:25:11+00:00 app[web.1]:   from script/rails:6:in `require'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:55:in `block in &lt;top (required)&gt;'
  2013-04-08T03:25:11+00:00 app[web.1]:   from script/rails:6:in `&lt;main&gt;'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:50:in `tap'
  2013-04-08T03:25:11+00:00 app[web.1]:   from /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/commands.rb:50:in `&lt;top (required)&gt;'
  2013-04-08T03:25:13+00:00 heroku[web.1]: Process exited with status 1
  2013-04-08T03:25:13+00:00 heroku[web.1]: State changed from starting to crashed
  2013-04-08T03:30:49+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path=/ host=********.herokuapp.com fwd="115.79.161.252" dyno= connect= service= status=503 bytes=
  2013-04-08T03:30:49+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path=/favicon.ico host=********.herokuapp.com fwd="115.79.161.252" dyno= connect= service= status=503 bytes=
  2013-04-08T03:30:50+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path=/ host=********.herokuapp.com fwd="115.79.161.252" dyno= connect= service= status=503 bytes=
  2013-04-08T03:30:51+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path=/favicon.ico host=********.herokuapp.com fwd="115.79.161.252" dyno= connect= service= status=503 bytes=
  </code></pre>
  
  <p>Some similar questions I've seen suggest running <code>heroku run rake db:migrate</code>, which gives me this output:</p>
  
  <pre><code>Running `rake db:migrate` attached to terminal... up, run.5112
  DEPRECATION WARNING: You have Rails 2.3-style plugins in vendor/plugins! Support for these plugins will be removed in Rails 4.0. Move them out and bundle them in your Gemfile, or fold them in to your app as lib/myplugin/* and config/initializers/myplugin.rb. See the release notes for more on this: http://weblog.rubyonrails.org/2012/1/4/rails-3-2-0-rc2-has-been-released. (called from &lt;top (required)&gt; at /app/Rakefile:7)
  DEPRECATION WARNING: You have Rails 2.3-style plugins in vendor/plugins! Support for these plugins will be removed in Rails 4.0. Move them out and bundle them in your Gemfile, or fold them in to your app as lib/myplugin/* and config/initializers/myplugin.rb. See the release notes for more on this: http://weblog.rubyonrails.org/2012/1/4/rails-3-2-0-rc2-has-been-released. (called from &lt;top (required)&gt; at /app/Rakefile:7)
  rake aborted!
  no such file to load -- nokogiri
  /app/lib/tasks/pivotal.rake:8:in `require'
  /app/lib/tasks/pivotal.rake:8:in `&lt;top (required)&gt;'
  /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:425:in `load'
  /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:425:in `block in load_tasks'
  /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:425:in `each'
  /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/engine.rb:425:in `load_tasks'
  /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/application.rb:145:in `load_tasks'
  /app/vendor/bundle/ruby/1.9.1/gems/railties-3.2.12/lib/rails/railtie/configurable.rb:30:in `method_missing'
  /app/Rakefile:7:in `&lt;top (required)&gt;'
  (See full trace by running task with --trace)
  </code></pre>
  
  <p>The line <code>no such file to load -- nokogiri</code> looks like it might be the culprit but I can't figure out how to fix it; I've tried running <code>bundle install</code>, <code>bundle update</code>, restarting heroku with <code>heroku restart</code> and all kinds of other guess-based solutions that I can't remember now but it's still not working!</p>
  
  <p>Here's my Gemfile:</p>
  
  <pre><code>source 'https://rubygems.org'
  
  gem 'rails', '3.2.12'
  gem 'bootstrap-sass'
  gem 'bcrypt-ruby', '3.0.1'
  gem 'paperclip', '~&gt; 3.4.1'
  gem 'nokogiri'
  
  gem "watu_table_builder", require: "table_builder"
  
  group :development, :test do
    gem 'sqlite3', '1.3.5'
    gem 'rspec-rails', '2.13.0'
    gem 'guard-rspec', '1.2.1'
    gem 'guard-spork', :github =&gt; 'guard/guard-spork'
    gem 'spork', '0.9.2'
    gem 'factory_girl_rails', '4.1.0', :require =&gt; false
  end
  
  group :development do
    gem 'annotate'
  end
  
  # Gems used only for assets and not required
  
  # in production environments by default.
  
  group :assets do
    gem 'sass-rails',   '3.2.5'
    gem 'coffee-rails', '3.2.2'
    gem 'uglifier', '1.2.3'
  end
  
  gem 'jquery-rails', '2.0.2'
  
  group :test do
    gem 'capybara', '1.1.2'
    # Gems specific to Mac OS X:
    gem 'capybara', '1.1.2'
    gem 'rb-fsevent', '0.9.1', :require =&gt; false
    gem 'growl', '1.0.3'
  end
  
  group :production do
    gem 'pg', '0.12.2'
  end
  </code></pre>