cronjob in docker container cannot connect to other container

I want to use cronjob to run a script, which is to fetch data from news api and feed it into postegres which is located in other container.

so the simplified architecture is

 app(in container) -> postegres(in container)

the cronjob script is inside app, and it will fetch data and then send to postegres.

in my crontab is

* * * * * cd /tourMamaRoot/tourMama/cronjob && fetch_news.py >> /var/log/cron.log 2>&1

i can run it successfully by manually run the script, but when i put it in crontab , it shows the error.

 File "/usr/local/lib/python3.6/dist-packages/django/db/backends/base/base.py", line 195, in connect
    self.connection = self.get_new_connection(conn_params)
  File "/usr/local/lib/python3.6/dist-packages/django/db/backends/postgresql/base.py", line 178, in get_new_connection
    connection = Database.connect(**conn_params)
  File "/usr/local/lib/python3.6/dist-packages/psycopg2/__init__.py", line 126, in connect
    conn = _connect(dsn, connection_factory=connection_factory, **kwasync)
django.db.utils.OperationalError: could not connect to server: No such file or directory
    Is the server running locally and accepting
    connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

seems it only look for database locally if use crontab, how can i set it to put data into other container like i manually run the script?

Info:

my docker container for app is Ubuntu version 18.04 , and the following is my docker file for app

FROM ubuntu:18.04
MAINTAINER Eson

ENV PYTHONUNBUFFERED 1
ENV DEBIAN_FRONTEND=noninteractive

EXPOSE 8000

# Setup directory structure
RUN mkdir /tourMamaRoot
WORKDIR /tourMamaRoot/tourMama/

COPY tourMama/requirements/base.txt /tourMamaRoot/base.txt
COPY tourMama/requirements/dev.txt /tourMamaRoot/requirements.txt

# install Python 3
RUN apt-get update && apt-get install -y 
        software-properties-common
RUN add-apt-repository ppa:deadsnakes/ppa
RUN apt-get update && apt-get install -y 
    python3.7 
    python3-pip
RUN python3.7 -m pip install pip
RUN apt-get update && apt-get install -y 
    python3-distutils 
    python3-setuptools

# install Postgresql
RUN apt-get -y install wget ca-certificates
RUN wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add -
RUN sh -c echo deb http://apt.postgresql.org/pub/repos/apt/ `lsb_release -cs`-pgdg main >> /etc/apt/sources.list.d/pgdg.list
RUN apt-get update
RUN apt-get install -y postgresql postgresql-contrib

# Install some dep
RUN apt-get install net-tools
RUN apt-get install -y libpq-dev python-dev

RUN pip3 install -r /tourMamaRoot/requirements.txt

# Copy application
COPY ./tourMama/ /tourMamaRoot/tourMama/

docker compose file:

version: '3'

services:
  app:
    build:
      # current directory
      # if for dev, need to have Dockerfile.dev in folder
      dockerfile: docker/dev/Dockerfile
      context: .
    ports:
      #host to image
      - "8000:8000"
    volumes:
      # map directory to image, which means if something changed in
      # current directory, it will automatically reflect on image,
      # don't need to restart docker to get the changes into effect
      - ./tourMama:/tourMamaRoot/tourMama
    command: >
      sh -c "python3 manage.py wait_for_db &&
             python3 manage.py makemigrations &&
             python3 manage.py migrate &&
             python3 manage.py runserver 0.0.0.0:8000 &&
             sh initial_all.sh"
    environment:
      - DB_HOST=db
      - DB_NAME=app
      - DB_USER=postgres
      - DB_PASS=supersecretpassword

    depends_on:
      - db
      - redis

  db:
    image: postgres:11-alpine
    ports:
      #host to image
      - "5432:5432"
    environment:
      - POSTGRES_DB=app
      - POSTGRES_USER=postgres
      - POSTGRES_PASSWORD=supersecretpassword

  redis:
    image: redis:5.0.5-alpine
    ports:
      #host to image
      - "6379:6379"

#    command: ["redis-server", "--appendonly", "yes"]
#    hostname: redis
#    networks:
#      - redis-net
#    volumes:
#      - redis-data:/data

and my cronjob script is:

import os
import sys
import django
from django.db import IntegrityError
from newsapi.newsapi_client import NewsApiClient
sys.path.append("../")
os.environ.setdefault("DJANGO_SETTINGS_MODULE", "tourMama.settings")
django.setup()
from news.models import News
from tourMama_app.models import Category
from config.script import categorization_loader

load_category = categorization_loader.load_category_data("catagorization.yml")
categories = list(load_category.keys())
countries = ["us", "gb"]

# Init
newsapi = NewsApiClient(api_key='secret')

for category in categories:
    for country in countries:
        category_lower = category.lower()
        category_obj = Category.objects.filter(
            category=category,
        ).get()

        top_headlines = newsapi.get_top_headlines(q='',
                                                  # sources=object'bbc-news,the-verge',
                                                  category=category_lower,
                                                  language='en',
                                                  page_size=100,
                                                  country=country
                                                  )

        for article in top_headlines.get("articles"):
            try:
                News.objects.create(
                    source=article["source"].get("name") if article["source"] else None,
                    title=article.get("title"),
                    author=article.get("author"),
                    description=article.get("description"),
                    url=article.get("url"),
                    urlToImage=article.get("urlToImage"),
                    published_at=article.get("publishedAt"),
                    content=article.get("content"),
                    category=category_obj
                )

            except IntegrityError:
                print("data already exist")

            else:
                print("data insert successfully")

and if needed, my django setting file is as following:

"""
Django settings for tourMama project.

Generated by 'django-admin startproject' using Django 2.2.1.

For more information on this file, see
https://docs.djangoproject.com/en/2.2/topics/settings/

For the full list of settings and their values, see
https://docs.djangoproject.com/en/2.2/ref/settings/
"""

import os

# Build paths inside the project like this: os.path.join(BASE_DIR, ...)
BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
TEMPLATE_DIR = os.path.join(BASE_DIR,"templates")

# Quick-start development settings - unsuitable for production
# See https://docs.djangoproject.com/en/2.2/howto/deployment/checklist/

# SECURITY WARNING: keep the secret key used in production secret!
SECRET_KEY = 'd084cm20*x*&s&w)vq+7*teea540yny+fyi^dh57nxiff&a#25'

# SECURITY WARNING: don't run with debug turned on in production!
DEBUG = True

COMPRESS_ENABLED = False
COMPRESS_CSS_HASHING_METHOD = 'content'
COMPRESS_FILTERS = {
    'css':[
        'compressor.filters.css_default.CssAbsoluteFilter',
        'compressor.filters.cssmin.rCSSMinFilter',
    ],
    'js':[
        'compressor.filters.jsmin.JSMinFilter',
    ]
}
HTML_MINIFY = False
KEEP_COMMENTS_ON_MINIFYING = False

ALLOWED_HOSTS = ['0.0.0.0', "127.0.0.1"]


# Application definition

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'channels',
    'bootstrap3',
    'tourMama_app',
    'account',
    'posts',
    'group',
    'news',
    'statistics',
    'compressor',
]

AUTH_USER_MODEL = "account.UserProfile"

MIDDLEWARE = [
    'django.middleware.gzip.GZipMiddleware',
    'htmlmin.middleware.HtmlMinifyMiddleware',
    'htmlmin.middleware.MarkRequestMiddleware',

    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
]

ROOT_URLCONF = 'tourMama.urls'

TEMPLATES = [
    {
        'BACKEND': 'django.template.backends.django.DjangoTemplates',
        'DIRS': [TEMPLATE_DIR,],
        'APP_DIRS': True,
        'OPTIONS': {
            'context_processors': [
                'django.template.context_processors.debug',
                'django.template.context_processors.request',
                'django.contrib.auth.context_processors.auth',
                'django.contrib.messages.context_processors.messages'   ,
            ],
        },
    },
]

WSGI_APPLICATION = 'tourMama.wsgi.application'
ASGI_APPLICATION = 'tourMama.routing.application'

# https://stackoverflow.com/questions/56480472/cannot-connect-to-redis-container-from-app-container/56480746#56480746
CHANNEL_LAYERS = {
    'default': {
        'BACKEND': 'channels_redis.core.RedisChannelLayer',
        'CONFIG': {
            "hosts": [('redis', 6379)],
        },
    },
}


# Database
# https://docs.djangoproject.com/en/2.2/ref/settings/#databases

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'HOST': os.environ.get('DB_HOST'),
        'NAME': os.environ.get('DB_NAME'),
        'USER': os.environ.get('DB_USER'),
        'PASSWORD': os.environ.get('DB_PASS')
    }
}


# Password validation
# https://docs.djangoproject.com/en/2.2/ref/settings/#auth-password-validators

AUTH_PASSWORD_VALIDATORS = [
    {
        'NAME': 'django.contrib.auth.password_validation.UserAttributeSimilarityValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.MinimumLengthValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.CommonPasswordValidator',
    },
    {
        'NAME': 'django.contrib.auth.password_validation.NumericPasswordValidator',
    },
]

STATICFILES_FINDERS = (
    'django.contrib.staticfiles.finders.FileSystemFinder',
    'django.contrib.staticfiles.finders.AppDirectoriesFinder',
    # other finders..
    'compressor.finders.CompressorFinder',
)

CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
        'LOCATION': '127.0.0.1:11211',
    }
}

# Internationalization
# https://docs.djangoproject.com/en/2.2/topics/i18n/

LANGUAGE_CODE = 'en-us'

TIME_ZONE = 'UTC'

USE_I18N = True

USE_L10N = True

USE_TZ = True


# Static files (CSS, JavaScript, Images)
# https://docs.djangoproject.com/en/2.2/howto/static-files/


STATIC_URL = '/static/'
STATICFILES_DIRS = [os.path.join(BASE_DIR, 'static'),]
STATIC_ROOT = os.path.join(BASE_DIR,"static_root")

MEDIA_URL = '/media/'
MEDIA_ROOT = os.path.join(BASE_DIR, 'media')

LOGIN_REDIRECT_URL = "home:index"
LOGOUT_REDIRECT_URL = "home:index"

Source: StackOverflow