title: Can't launch simple Sinatra app using rackup and jRuby (no response from web server)
body: <p>I've got a Sinatra "hello world" app that I am trying to run using jRuby. It works when I run the app, but not when I run rackup. Can anyone tell me what is going on here?</p>
  
  <p>Here's the app, in a file 'app.rb':</p>
  
  <pre><code>require 'rubygems'
  require 'bundler/setup'
  require 'sinatra'
  
  configure do
    set :bind, '0.0.0.0'
  end
  
  get '/' do
    'Boo!'
  end
  </code></pre>
  
  <p>I can run this using <code>bundle exec ruby app.rb</code> and it works fine:</p>
  
  <pre><code>jonea@centos7andy[~/andy/sinatra_sand_jruby]%: bundle exec ruby app.rb
  [2015-01-12 10:36:06] INFO  WEBrick 1.3.1
  [2015-01-12 10:36:06] INFO  ruby 1.9.3 (2014-12-09) [java]
  == Sinatra/1.4.5 has taken the stage on 4567 for development with backup from WEBrick
  [2015-01-12 10:36:06] INFO  WEBrick::HTTPServer#start: pid=31654 port=4567
  </code></pre>
  
  <p>Here is my config.ru to call the above program:</p>
  
  <pre><code>require 'rubygems'
  require 'bundler/setup'
  require 'sinatra'
  require './app'
  
  run Sinatra::Application
  </code></pre>
  
  <p>If I run this, it appears to work, but I can't access the server using a web browser:</p>
  
  <pre><code>jonea@centos7andy[~/andy/sinatra_sand_jruby]%: bundle exec rackup -p4567
  [2015-01-12 10:29:06] INFO  WEBrick 1.3.1
  [2015-01-12 10:29:06] INFO  ruby 1.9.3 (2014-12-09) [java]
  [2015-01-12 10:29:06] INFO  WEBrick::HTTPServer#start: pid=31553 port=4567
  </code></pre>
  
  <p>I note the suspicious lack of "Sinatra has taken the stage..."</p>