How to run Flask AND celery in one container?

I want to deploy my little web application with docker on digitalocean. Problem is, that i didn't separate flask + celery, so everything is in one container. Everytime i run docker-compose up the web container crashses ("exited with code 0").

The project structure looks as follows:

.
.
├── docker-compose.yml
├── nginx
│   ├── dockerfile
│   └── nginx.conf
└── web
    ├── app.ini
    ├── bot
    │   ├── __init__.py
    │   ├── main.py
    │   ├── __pycache__
    │   └── timer.py
    ├── celeryd.pid
    ├── config.py
    ├── dockerfile
    ├── dockerignore
    ├── flask_app.py
    ├── __init__.py
    ├── requirements.txt
    ├── tasks.py
    └── webapp
        ├── bot
        ├── __init__.py
        ├── models.py
        ├── __pycache__
        ├── static
        ├── templates
        └── users

This is the docker-compose.yml:

version: "3.7"

services:

  rabbitmq:
    image: rabbitmq:3-management
    hostname: rabbitmq
    container_name: rabbitmq
    environment:
      RABBITMQ_ERLANG_COOKIE: 'SWQOKODSQALRPCLNMEQG'
      RABBITMQ_DEFAULT_USER: 'user123'
      RABBITMQ_DEFAULT_PASS: 'password123'
      RABBITMQ_DEFAULT_VHOST: '/webapp'
    ports:
      - "15672:15672"
      - "5672:5672"
    volumes:
      - rabbitmq_storage:/var/lib/rabbitmq
    networks:
      netzwerk123:
        aliases:
          - rabbitmq

  db:
    image: mariadb
    restart: always
    container_name: db
    environment:
      MYSQL_ROOT_PASSWORD: 'password123'
      MYSQL_USER: 'user123'
      MYSQL_PASSWORD: 'password123'
      MYSQL_DATABASE: 'webapp'
    ports:
      - "3306:3306"
    volumes:
      - db_storage:/var/lib/mysql
    networks:
      netzwerk123:
        aliases:
          - db


  nginx:
    build: ./nginx  
    container_name: nginx
    restart: always
    ports:  
      - "80:80"
    networks:
      netzwerk123:
        aliases:
          - ngnix


  web:
    build: ./web  
    container_name: web
    hostname: web
    restart: always
    environment:    
      FLASK_DEBUG: 'True'
      FLASK_APP: 'flask_app.py'
    command: celery -A tasks.celery worker --loglevel=info --detach
    expose:
      - 8080
    networks:
      netzwerk123:
        aliases:
          - web
    depends_on:     
      - nginx
      - db
      - rabbitmq
    links:
      - rabbitmq
    tty: true
    stdin_open: true


  adminer:        #only for development purposes
    image: adminer
    container_name: adminer
    restart: always
    ports:
      - "8081:8080"
    depends_on:
      - db
    networks:
      netzwerk123:
        aliases:
          - adminer



volumes:                                    
  db_storage:
  rabbitmq_storage:

networks:
  netzwerk123:

If i comment "command: celery -A tasks.celery worker --loglevel=info --detach" everything runs just fine, since celery is not running. Webpage is fully functioning, database is active. Everything's fine, except for celery.

By uncommenting the command line, docker throws the "web exited with error code 0".

I guess this is due to the fact, that docker exits the container after successfully executing the command. So there are two problems i face:

1) How to run celery in the background of the same container of celery, so that there won't appear the error code 0?

2) How to run celery AND flask parallel in the container?

-> i already tried the following, but same error:

command: bash -c "uwsgi app.ini && celery -A tasks.celery worker --loglevel=info --detach"

Any help is highly appreciated :)

EDIT: The reason i put celery + flask in one container is my task.py. In here i import all sqlalchemy models from the web.webapp.models. So i need to have access to the flask directory and currently i don't see a way how to separate this into two containers