title: Error: Bad Gateway 502 when opening Google App Engine Python Domain
body: <p>When I'm visiting my website (<a href="https://osm-messaging-platform.appspot.com" rel="noreferrer">https://osm-messaging-platform.appspot.com</a>), I get this error on the main webpage: </p>
  
  <pre><code>502 Bad Gateway. nginx/1.14.0 (Ubuntu).
  </code></pre>
  
  <p>It's really weird, since when I run it locally</p>
  
  <pre><code>python app.py
  </code></pre>
  
  <p>I get no errors, and my app and the website load fine.</p>
  
  <p>I've already tried looking it up, but most of the answers I've found on stack overflow either have no errors or don't relate to me. Here is the error when I look at my GCloud logs:</p>
  
  <pre><code>019-02-07 02:07:05 default[20190206t175104]  Traceback (most recent 
  call last):    File "/env/lib/python3.7/site- 
  packages/gunicorn/arbiter.py", line 583, in spawn_worker      
  worker.init_process()    File "/env/lib/python3.7/site- 
  packages/gunicorn/workers/gthread.py", line 104, in init_process      
  super(ThreadWorker, self).init_process()    File 
  "/env/lib/python3.7/site-packages/gunicorn/workers/base.py", line 
  129, in init_process      self.load_wsgi()    File 
  "/env/lib/python3.7/site-packages/gunicorn/workers/base.py", line 
  138, in load_wsgi      self.wsgi = self.app.wsgi()    File 
  "/env/lib/python3.7/site-packages/gunicorn/app/base.py", line 67, in 
  wsgi      self.callable = self.load()    File 
  "/env/lib/python3.7/site-packages/gunicorn/app/wsgiapp.py", line 52, 
  in load      return self.load_wsgiapp()    File 
  "/env/lib/python3.7/site-packages/gunicorn/app/wsgiapp.py", line 41, 
  in load_wsgiapp      return util.import_app(self.app_uri)    File 
  "/env/lib/python3.7/site-packages/gunicorn/util.py", line 350, in 
  import_app      __import__(module)  ModuleNotFoundError: No module 
  named 'main'
  2019-02-07 02:07:05 default[20190206t175104]  [2019-02-07 02:07:05 
  +0000] [25] [INFO] Worker exiting (pid: 25)
  2019-02-07 02:07:05 default[20190206t175104]  [2019-02-07 02:07:05 
  +0000] [8] [INFO] Shutting down: Master
  2019-02-07 02:07:05 default[20190206t175104]  [2019-02-07 02:07:05 
  +0000] [8] [INFO] Reason: Worker failed to boot.
  </code></pre>
  
  <p>And here are the contents of my app.yaml file:</p>
  
  <pre><code>runtime: python37
  
  handlers:
   # This configures Google App Engine to serve the files in the app's 
  static
   # directory.
   - url: /static
   static_dir: static
  
  
  - url: /.*
    script: auto
  </code></pre>
  
  <p>I expected it to show my website, but it didn't. Can anyone help?</p>