.env.prod

# everything in .env including this below
...
DB_HOST=db
DATASBASE=
...

.env.prod.db

POSTGRES_USER=
POSTGRES_PASSWORD=
POSTGRES_DB=

docker-compose.yml

version: '3.7'
services:
  web:
    build: ./
    command: 'gunicorn internplug.wsgi:application --bind 0.0.0.0:8000'
    container_name: internplug
    volumes:
      - './:/usr/src/app/'
    ports:
      - '8000:8000'
    env_file: 
      - ./.env.prod.db
    depends_on:
      - db
  db:
    image: 'postgres'
    container_name: internplug_db
    volumes:
      - 'postgres_data:/var/lib/postgresql/data/'
    env_file: 
      - ./.env.prod.db
volumes:
  postgres_data: null

entrypoint.prod.sh

#!/bin/sh

if [ "$DATABASE" = "internplug2" ]
then
    echo "Waiting for postgres..."

    while ! nc -z $SQL_HOST $SQL_PORT; do
      sleep 0.1
    done

    echo "PostgreSQL started"
fi
python manage.py makemigrations
python manage.py makemigrations accounts 
python manage.py makemigrations emails
python manage.py makemigrations jobs
python manage.py makemigrations main
exec "$@"