title: Web process failed to bind to $PORT within 60 seconds of launch
body: <p>Can someone explain to me this error message on Heroku?  App works fine locally but has never succeeded online</p>
  
  <pre><code>heroku[slug-compiler]: Slug compilation started
  heroku[slug-compiler]: Slug compilation finished
  heroku[web.1]: State changed from crashed to starting
  heroku[web.1]: Starting process with command `python app.py ${PORT}`
  app[web.1]:  * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
  heroku[web.1]: Error R10 (Boot timeout) -&gt; Web process failed to bind to $PORT within 60 seconds of launch
  </code></pre>
  
  <p>The app itself is not very complicated</p>
  
  <pre><code>from flask import Flask, render_template
  app = Flask(__name__, static_folder='static') 
  
  @app.route('/')
  def hello_world():
      return render_template('index.html')
  
  if __name__ == '__main__':
      from os import environ
      app.run(debug=False, port=environ.get("PORT", 5000))
  </code></pre>