Docker not persisting postgres volume [django] - django

Question

There are many questions that have been asked on here about similar issues that I went through such as this, this, this and this that are very similar but none of the solutions there solve my problem. Please don't close this question.
Problem:
I am running django with nginx and postgres on docker. Secret information is stored in an .env file. My postgres data is not persisting with docker-compose up/start and docker-compose down/stop/restart.
This is my docker-compose file:
version: '3.7'
services:
web:
build: ./app
command: gunicorn umngane_project.wsgi:application --bind 0.0.0.0:8000
volumes:
- ./app/:/usr/src/app/
expose:
- 8000
environment:
- SECRET_KEY=${SECRET}
- SQL_ENGINE=django.db.backends.postgresql
- SQL_DATABASE=postgres
- SQL_USER=${POSTGRESQLUSER}
- SQL_PASSWORD=${POSTGRESQLPASSWORD}
- SQL_HOST=db
- SQL_PORT=5432
- SU_NAME=${SU_NAME}
- SU_EMAIL=${SU_EMAIL}
- SU_PASSWORD=${SU_PASSWORD}
depends_on:
- db
db:
image: postgres:11.2-alpine
volumes:
- postgres_data:/var/lib/postgresql/data/
nginx:
build: ./nginx
volumes:
- static_volume:/usr/src/app/assets
ports:
- 1337:80
depends_on:
- web
volumes:
postgres_data:
external: true # I tried running without this and the result is the same
static_volume:
My entrypoint scipt is this:
python manage.py flush --no-input
python manage.py makemigrations
python manage.py migrate
python manage.py createsuperuser --user "${SU_NAME}" --email "${SU_EMAIL}" --password "${SU_PASSWORD}"
python manage.py collectstatic --no-input
exec "$#"
where createsuperuser is a custom module that creates a superuser in the application.
This setup is not persisting the information in postgres_data.
Additional information:
Before doing anything, I check to see that there is no volume named postgres_data using docker volume ls and get just that.
At which point I run docker-compose up -d/docker-compose up -d --build and everything works out fine with no errors.
I run docker inspect postgres_data and it shows "CreatedAt": "X1"
I am able to login as the superuser. I proceed to create admin users, logout as the superuser and then login as any of the admin users with no problem. I run docker exec -it postgres_data psql -U <postgres_user> to make sure the admin users are in the database and find just that.
At which point I proceed to run docker-compose down/docker-compose stop with no problem. I run docker volume ls and it shows that postgres_data is still there.
I run docker inspect postgres_data and it shows "CreatedAt": "X2"
To test that everything works as expected I run docker-compose up -d/docker-compose up -d --build/docker-compose start/docker-compose restart.
I run docker inspect postgres_data and it shows "CreatedAt": "X3"
At which point I proceed to try and login as an admin user and am not able to. I run docker exec -it postgres_data psql -U <postgres_user> again but this time only see the superuser, no admin users.
(Explanation: I am here using the forward slash to show all the different things I tried on different attempts. I tried every combination of commands shown here.)

Answer 1

The issue is you run "flush" in your entrypoint script which clears the database. The entrypoint will run whenever you boot or recreate the container.

Answer 2

One way of having persistent data is specifying an actual path on the disk instead of creating a volume:
...
db:
image: postgres:11.2-alpine
volumes:
- "/local/path/to/postgres/data:/var/lib/postgresql/data/"
...
This way, the container's postgres data location is mapped to a path you specify. This way, the data persists directly on disk unless purposely deleted.
A docker volume, as far as I know, is going to be removed on container removal.