app.py

from flask import Flask, redirect, url_for
from celery import Celery
from celery import Task
from subprocess import PIPE, Popen
import logging, os
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)

# Running locally:

# Start:
# docker run -d -p 6379:6379 redis
# celery -A app.celery worker --loglevel=info
# python app.py

# Web:
# http://127.0.0.1:5000/docker to run celery task
# http://127.0.0.1:5000/result to see result

# This method is copied from here: https://flask.palletsprojects.com/en/1.0.x/patterns/celery/
# No need to think about it!
def make_celery(app):
    celery = Celery(
        app.import_name,
        backend=app.config['CELERY_RESULT_BACKEND'],
        broker=app.config['CELERY_BROKER_URL']
    )
    celery.conf.update(app.config)

    class ContextTask(celery.Task):
        def __call__(self, *args, **kwargs):
            with app.app_context():
                return self.run(*args, **kwargs)

    celery.Task = ContextTask
    return celery

flask_app = Flask(__name__)
flask_app.config.update(
    CELERY_BROKER_URL='redis://localhost:6379/1',
    CELERY_RESULT_BACKEND='redis://localhost:6379/0'
)
celery = make_celery(flask_app)

@flask_app.route("/docker")
def docker():
    # starts new task to run the container:
    run_container.delay()
    return f"Container started."

# check results on another page:
@flask_app.route('/result')
def result():
    if os.path.isfile('res.txt'):
        f = open("res.txt", "r")
        return f.read()
    else:
        return f"Still processing."

@celery.task(name='celery_task.run_container')
def run_container():
    process = Popen(["docker", "run", "hello-world"], stdout=PIPE)
    stdout, stderr = process.communicate()
    # write output in 'db' (here text file)
    with open('res.txt','w') as f:
        f.write(str(stdout))

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