Running cron job inside container with python code and postgres database - postgresql

Question

I am new into docker, and I have created a container with python + postgres, which runs a python script that collects some data and writes it down on the SQL database. Now, I need to set this job to run each day. And then the nightmare started. I did not manage to create a separate container for this job, so I tried to create a file and copy it into the container via DockerFile (see this one down). I did not manage to run cron as entry-point for the container because then my database was not mounted. So, I create the container, access it, give full permissions to /var/www/html, and create the database table. And then I run cron. No erro, but nothing happens, no log is written on /var/log/cron.log. Here my files:
Dockerfile:
FROM postgres:latest
USER root
RUN apt-get update && apt-get install -y python3 python3-pip
RUN apt-get -y install cron nano
RUN apt-get -y install postgresql-server-dev-10 gcc python3-dev musl-dev
RUN pip3 install psycopg2 \
bs4 \
requests \
pytz
COPY temp-alerts-cron /etc/cron.d/temp-alerts-cron
RUN chmod 0777 /etc/cron.d/temp-alerts-cron
RUN chmod gu+rw /var/run/
RUN chmod gu+s /usr/sbin/cron
RUN touch /var/log/cron.log
RUN chmod 0777 /var/log/cron.log
RUN crontab /etc/cron.d/temp-alerts-cron
USER postgres
EXPOSE 5432
VOLUME ["/etc/postgresql", "/var/log/postgresql", "/var/lib/postgresql"]
The temp-alers-cron:
20 13 * * * root /var/www/html/run.sh >> /var/log/cron.log 2>&1
# Don't remove the empty line at the end of this file. It is required to run the cron job
And the called script:
echo 'inside thingy' >> /var/log/cron.log 2>&1
python3 /var/www/html/nuria_main.py
In case it is needed, here the docker-compose.yml:
services:
postgres:
container_name: 'temp-postgres'
build: # build the image from Dockerfile
context: ${PWD}
volumes: # bind mount volume for Postgres data
- pg-data:/var/lib/postgresql/data
- ./python-app:/var/www/html
restart: unless-stopped
environment:
- POSTGRES_USR=xxadmin
- POSTGRES_DB=tempdb
- POSTGRES_PASSWORD=secret
expose:
- "5432"
networks:
kong:
networks:
kong:
external:
name: kong_net
volumes:
pg-data:
Hope somebody knows what I am doing wrong. I do not get any log or error, so i am lost.
Thanks!