title: Heroku error code=H10 status=503 when deploying python flask app
body: <p>I get this error code:</p>
  <blockquote>
  <p>rashed 2020-08-27T00:35:29.293812+00:00 heroku[router]: at=error
  code=H10 desc=&quot;App crashed&quot; method=GET path=&quot;/&quot;
  host=song-recommender-michaelwzhu.herokuapp.com
  request_id=516f57c9-167b-47c0-86fb-3258aa046768 fwd=&quot;24.4.72.198&quot;
  dyno= connect= service= status=503 bytes= protocol=https</p>
  </blockquote>
  <p>My python flask app works when hosted locally, but displays application error when deployed on Heroku.</p>
  <p>My <code>app.py</code> file:</p>
  <pre><code>app = Flask(__name__)
  
  *code*
  
  if __name__ == '__main__':
  app.run(debug=True)
  </code></pre>
  <p>My <code>requirements.txt</code> file:</p>
  <pre><code>click==7.1.2
  Flask==1.1.2
  gunicorn==20.0.4
  itsdangerous==1.1.0
  Jinja2==2.11.2
  MarkupSafe==1.1.1
  Werkzeug==1.0.1
  </code></pre>
  <p>My <code>Procfile</code>:</p>
  <pre><code>web: gunicorn app:app
  </code></pre>