[FIXED] Calling flask app from another flask app locally

Issue

I have two Flask apps (A and B). App A is running locally on port 5000 and makes a post request to app B running on port 5002 like such:

headers = {
    'accept': 'application/type',
    'Content-Type': 'application/json'
}

data = '{"test_string": "test input string", "flatten": true}'

response = requests.post('http://localhost:5002/endpoint', headers=headers, data=data)

and the response back is:

Max retries exceeded with url: /endpoint/ Failed to establish a new connection: [Errno 111] Connection refused

I opened my terminal and tried this curl request:

curl -X 'POST' 'http://localhost:5002/endpoint/' -H 'accept: application/json' -H 'Content-Type: application/json' -d '{"test_string": "test input string", "flatten": true}'

and it returns the correct response from app B

I figured maybe there was a problem with how I formatted the request on app A since curl was working and I tested the 3 lines I had on app A just using python from my terminal and it worked in my python terminal.

The only variable left is app A being a flask app running locally since that code snippet runs in python terminal. Is there some problem with calling app B from app A with both apps running locally on different ports?

---

UPDATE: Ok, I have narrowed down the the issue to something with docker-compose and Redis. Here is how to replicate it:

APP B: app.py

from flask import Flask, abort
from flask_restx import Api, Resource, fields

app = Flask(__name__)
api = Api(app, version='1.0', title='something',
          description='something',
          )

ns = api.namespace('parse', description='something')

parse_raw = api.model('parse', {
    'input_string': fields.String(required=True, description='string')
})


@ns.route('/')
class Parser(Resource):
    @ns.doc('parse')
    @ns.expect(parse_raw)
    def post(self):
        '''Parse'''
        try:
            s = "yes"
        except Exception:
            abort(400, 'unsupported')

        return s, 200


if __name__ == '__main__':
    app.run(debug=True, host='0.0.0.0', port=5002)

APP A: app.py

from flask import Flask
from flask_restx import Api, Resource
import requests

app = Flask(__name__)
api = Api(app, version='1.0', title='something',
          description='something',
          )

ns = api.namespace('parse', description='something')


@ns.route('/')
class Parser(Resource):
    @ns.doc('parse')
    def get(self):
        '''Parse'''
        headers = {
            'accept': 'application/json',
            'Content-Type': 'application/json',
        }

        data = '{"input_string": "SELECT * FROM table1"}'
        response = requests.post('http://0.0.0.0:5002/parse/', headers=headers, data=data)

        return response.text, 200


if __name__ == '__main__':
    app.run(debug=True, host='0.0.0.0', port=5000)

docker-compose.yaml

version: '3'
services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - "5000:5000"
  redis:
    image: "redis:alpine"

Dockerfile

FROM python:3.6-alpine
WORKDIR /app

ENV PYTHONHASHSEED=1

RUN apk add --no-cache --update make
COPY requirements.txt requirements.txt
RUN pip install -r requirements.txt

COPY . .

CMD ["python3", "app.py"]

requirements.txt

redis
Flask~=1.1.2
flask-restx
tenacity
requests

you can run app B the normal way, how I run app A: docker-compose up --build

You can curl app B from a terminal: curl -X 'POST' \ 'http://localhost:5002/parse/' \ -H 'accept: application/json' \ -H 'Content-Type: application/json' \ -d '{ "input_string": "string" }'

and you can also run the code instead app A from a python terminal:

headers = {
            'accept': 'application/json',
            'Content-Type': 'application/json',
        }

        data = '{"input_string": "SELECT * FROM table1"}'
        response = requests.post('http://0.0.0.0:5002/parse/', headers=headers, data=data)

But app A CANNOT call app B

If you run app A by just running app.py it works fine, it only breaks using docker-compose + redis even though redis isnt even used in the example

Solution

Figured it out. Docker containers run on a different network so 'localhost' will not work. Dockerizing app B and deploying it to the same docker network as app A, and then changing 'localhost' to the container name of B on the network fixes it.

Answered By - user3831011