title: Zappa+Flask: A GET request to '/' yielded a 502 response code
body: <p>I am trying to deploy my flask app on aws lambda via zappa. And I am getting the following error when I do <code>zappa deploy dev</code>:</p>
  
  <pre><code>Calling deploy for stage dev..
  Downloading and installing dependencies..
   - sqlalchemy==1.3.16: Downloading
  100%|██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 1.24M/1.24M [00:00&lt;00:00, 6.06MB/s]
   - psycopg2-binary==2.8.5: Downloading
  100%|██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 2.94M/2.94M [00:00&lt;00:00, 8.30MB/s]
   - pandas==1.0.3: Using locally cached manylinux wheel
   - numpy==1.18.3: Using locally cached manylinux wheel
   - markupsafe==1.1.1: Downloading
  100%|██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 27.5k/27.5k [00:00&lt;00:00, 1.46MB/s]
  Packaging project as zip.
  Uploading prices-service-dev-1587997268.zip (44.2MiB)..
  100%|███████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 46.3M/46.3M [01:05&lt;00:00, 710kB/s]
  Scheduling..
  Scheduled prices-service-dev-zappa-keep-warm-handler.keep_warm_callback with expression rate(4 minutes)!
  Uploading prices-service-dev-template-1587997350.json (1.6KiB)..
  100%|██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 1.65k/1.65k [00:00&lt;00:00, 19.7kB/s]
  Waiting for stack prices-service-dev to create (this can take a bit)..
   75%|██████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████                                          | 3/4 [00:09&lt;00:03,  3.13s/res]
  Deploying API Gateway..
  Error: Warning! Status check on the deployed lambda failed. A GET request to '/' yielded a 502 response code.
  </code></pre>
  
  <p>When I do <code>zappa init</code>, it generates the following <code>zappa_settings.json</code> file:</p>
  
  <pre><code>{
      "dev": {
          "app_function": "main.app",
          "aws_region": "eu-central-1",
          "profile_name": "default",
          "project_name": "ps-zappa-test",
          "runtime": "python3.7",
          "s3_bucket": -MY_BUCKET_NAME-
      }
  }
  </code></pre>
  
  <p>and my <code>main.py</code> file is:</p>
  
  <pre><code>import os
  from app import create_app
  from config import config_by_name
  from app.extensions import db
  
  config_name = os.getenv("FLASK_CONFIG") or "default"
  app_config = config_by_name[config_name]
  app = create_app(app_config)
  
  db.create_all(app=app)
  
  if __name__ == '__main__':
      app.run()
  </code></pre>
  
  <p>My dependencies:</p>
  
  <pre><code>aniso8601==8.0.0
  argcomplete==1.11.1
  attrs==19.3.0
  beautifulsoup4==4.9.0
  boto3==1.12.46
  botocore==1.15.46
  certifi==2020.4.5.1
  cfn-flip==1.2.3
  chardet==3.0.4
  click==7.1.1
  docutils==0.15.2
  durationpy==0.5
  entsoe-py==0.2.13
  Flask==1.1.2
  flask-marshmallow==0.12.0
  flask-restx==0.2.0
  Flask-SQLAlchemy==2.4.1
  future==0.18.2
  gunicorn==20.0.4
  hjson==3.0.1
  idna==2.9
  importlib-metadata==1.6.0
  itsdangerous==1.1.0
  Jinja2==2.11.2
  jmespath==0.9.5
  jsonschema==3.2.0
  kappa==0.6.0
  MarkupSafe==1.1.1
  marshmallow==3.5.1
  marshmallow-sqlalchemy==0.23.0
  more-itertools==8.2.0
  numpy==1.18.3
  packaging==20.3
  pandas==1.0.3
  pip-tools==5.0.0
  placebo==0.9.0
  pluggy==0.13.1
  psycopg2-binary==2.8.5
  py==1.8.1
  pyparsing==2.4.7
  pyrsistent==0.16.0
  pytest==5.4.1
  python-dateutil==2.6.1
  python-dotenv==0.13.0
  python-slugify==4.0.0
  pytz==2019.3
  PyYAML==5.3.1
  requests==2.23.0
  s3transfer==0.3.3
  six==1.14.0
  soupsieve==2.0
  SQLAlchemy==1.3.16
  text-unidecode==1.3
  toml==0.10.0
  tqdm==4.45.0
  troposphere==2.6.0
  urllib3==1.25.9
  wcwidth==0.1.9
  Werkzeug==0.16.1
  wsgi-request-logger==0.4.6
  zappa==0.51.0
  zipp==3.1.0
  </code></pre>
  
  <p>When I do <code>zappa tail</code>, it gives:</p>
  
  <pre><code>Calling tail for stage dev..
  [1587996139600] Instancing..
  [1587996139773] Instancing..
  [1587996143093] OpenBLAS WARNING - could not determine the L2 cache size on this system, assuming 256k
  [1587996143255] OpenBLAS WARNING - could not determine the L2 cache size on this system, assuming 256k
  [1587996148073] [ERROR] OperationalError: (psycopg2.OperationalError) could not connect to server: Connection refused
  [1587996148073] Is the server running on host "localhost" (127.0.0.1) and accepting
  [1587996148073] TCP/IP connections on port 5432?
  [1587996148073] could not create socket: Address family not supported by protocol
      conn = _connect(dsn, connection_factory=connection_factory, **kwasync)nectption_noconnection
  [1587996148289] [ERROR] OperationalError: (psycopg2.OperationalError) could not connect to server: Connection refused
  [1587996148289] Is the server running on host "localhost" (127.0.0.1) and accepting
  [1587996148289] TCP/IP connections on port 5432?
  [1587996148289] could not create socket: Address family not supported by protocol
      conn = _connect(dsn, connection_factory=connection_factory, **kwasync)nectption_noconnection
  </code></pre>
  
  <p>Any suggestions on how this issue can be solved?</p>