Unable to deploy Flask App on Google App Engine getting an error "502 Bad Gateway"-CodePudding

I am trying to deploy a simple Flask application on the Google App Engine, Issue is that code is getting deployed without an error but when I access the URL of the deployed app then I get the error "502 Bad Gateway"

Logs

Below is the code I am using

app.yaml

runtime: custom
env: flex
entrypoint: gunicorn -b :$PORT main:app

runtime_config:
 python_version: 3

manual_scaling:
  instances: 1

resources:
  cpu: 1
  memory_gb: 1
  disk_size_gb: 10

Dockerfile

FROM ubuntu:18.04

RUN apt-get update \
    && apt-get install -y apt-utils \
    python3.6 \
    python3-pip
    
WORKDIR /app
COPY . /app
RUN pip3 install -r requirements.txt

ENTRYPOINT ["python3"]
CMD ["main.py"]

main.py

from flask import Flask, jsonify

app = Flask(__name__)

@app.route('/')
def index():
    return jsonify('Hello World')

if __name__ == '__main__':
    app.run(debug=True)

requirements.txt

Flask
gunicorn

CodePudding user response：

Posting @JohnHanley's comment for visibility.

The default port is 8080. Flask listens on port 5000. Change your code as follows: app.run(host='0.0.0.0', port=8080)