Docker losing Postgres server data when I shutdown the backend container - postgresql

Question

I've got the following docker-compose file and it serves up the application on port 80 fine.
version: '3'
services:
backend:
build: ./Django-Backend
command: gunicorn testing.wsgi:application --bind 0.0.0.0:8000 --log-level debug
expose:
- "8000"
volumes:
- static:/code/backend/static
env_file:
- ./.env.prod
nginx:
build: ./nginx
ports:
- 80:80
volumes:
- static:/static
depends_on:
- backend
db:
image: postgres
environment:
- POSTGRES_DB=postgres
- POSTGRES_USER=postgres
- POSTGRES_PASSWORD=postgres
volumes:
- postgres_data:/var/lib/postgresql/data/
volumes:
static:
postgres_data:
Once in there I can log into the admin and add an extra user which gets saved to the database as I can reload the page and the user is still there. Once I stop the backend docker container however that user is gone. Given Postgres is operating in a different container and I'm not bringing it down I'm unsure how stopping the backend container and restarting it is causing the data not to be available.
Thanks in advance.
EDIT:
I'm bringing up the docker container with the following command.
docker-compose -f docker-compose.prod.yml up -d
I'm bringing down the container by just using docker desktop and stopping the container.
I'm running DJANGO 3 for the backend and I've also tried adding a superuser in the terminal when the container is running:
# python manage.py createsuperuser
Username (leave blank to use 'root'): mikey
Email address:
Password:
Password (again):
This password is too common.
Bypass password validation and create user anyway? [y/N]: y
Superuser created successfully.
Which works and the user appears while the container is running. However, once again when I shut the container down via docker desktop and then restart it that user that was just created is gone.
FURTHER EDIT:
settings.py using dotenv "from dotenv import load_dotenv"
DATABASES = {
"default": {
"ENGINE": os.getenv("SQL_ENGINE"),
"NAME": os.getenv("SQL_DATABASE"),
"USER": os.getenv("SQL_USER"),
"PASSWORD": os.getenv("SQL_PASSWORD"),
"HOST": os.getenv("SQL_HOST"),
"PORT": os.getenv("SQL_PORT"),
}
}
with the .env.prod file having the following values:
DEBUG=0
DJANGO_ALLOWED_HOSTS=localhost 127.0.0.1 [::1]
SQL_ENGINE=django.db.backends.postgresql
SQL_DATABASE=postgres
SQL_USER=postgres
SQL_PASSWORD=postgres
SQL_HOST=db
SQL_PORT=5432
SOLUTION:
Read the comments to see the diagnosis by other legends but updated docker-compose file looks like this. Note the "depends_on" block.
version: '3'
services:
backend:
build: ./Django-Backend
command: gunicorn testing.wsgi:application --bind 0.0.0.0:8000 --log-level debug
expose:
- "8000"
volumes:
- static:/code/backend/static
env_file:
- ./.env.prod
depends_on:
- db
nginx:
build: ./nginx
ports:
- 80:80
volumes:
- static:/static
depends_on:
- backend
db:
image: postgres
environment:
- POSTGRES_DB=postgres
- POSTGRES_USER=postgres
- POSTGRES_PASSWORD=postgres
volumes:
- postgres_data:/var/lib/postgresql/data/
expose:
- "5432"
volumes:
static:
postgres_data:
FINAL EDIT:
Added the following code to my entrypoint.sh file to ensure Postgres is ready to accept connections by the backend container.
if [ "$DATABASE" = "postgres" ]
then
echo "Waiting for postgres..."
while ! nc -z $SQL_HOST $SQL_PORT; do
sleep 0.1
done
echo "PostgreSQL started"
fi