How to persist database file in project folder? - django

Question

My application gathers data and stores it in an SQLite database (located in ./data/db.sqlite3) that we want to exchange through our Git repo along with the code. When I dockerize the app, on each machine the data persists, yet not in the project folder itself.
docker-compose.yml:
version: "3.8"
services:
gcs:
build: .
volumes:
- type: bind
source: ./data
target: /data
ports:
- "8000:8000"
Docker file :
FROM python:3.8-slim-buster
WORKDIR /gcs
COPY requirements.txt requirements.txt
RUN apt-get update && apt-get install nginx vim binutils libproj-dev gdal-bin -y --no-install-recommends
RUN pip3 install -r requirements.txt
COPY . .
CMD python3 manage.py runserver 0.0.0.0:8000
It mounts the 'data' folder in projects folder to a data folder in the container. When I use Docker inspect the source folder corresponds with project database location:
"Mounts": [
{
"Type": "bind",
"Source": "/Users/rleblon/projects/gcsproject/data",
"Destination": "/data",
"Mode": "",
"RW": true,
"Propagation": "rprivate"
}
Yet somehow the persistent data is kept elsewhere, never ./data/db.sqlite3 itself gets updated on the host machine.
As I understand Docker creates a regular volume elsewhere and shares that between containers, but what's the point of specifying source and target when the source file was already copied into container? How can I get Docker to use the exact sqlite3 file I want, instead of creating a volume elsewhere and persisting a copy there?

Answer 1

It looks like you may be both copying your sqlite3 db into your image - via the line in your Dockerfile
COPY . .
which given your defined working directory in the Dockerfile
WORKDIR /gcs
and the looks of your directory structure, may copy the db to
/gcs/data
as well as mounting the same sqlite3 db via your docker-compose file in line
volumes:
- type: bind
source: ./data
target: /data
to
/data
in your running container of this image.
So you may have two versions of your data running in a container of this image: at
/gcs/data <-- copied over to the image in Dockerfile
/data <-- mounted as volume in docker-compose
Make sure you are not copying a version of the db into the image via your Dockerfile.
If your gcs service interacts with the version of your sqlite3 db located in /gcs/data, and not the mounted volume at /data, then any changes to the db would not persist after the container is destroyed.
On the other hand, if your app is pointing to the mounted volume version of your db at /data, then make sure the permissions set on your host / image allow for the db operations you desire.
Remember you are using a bind mount in your compose file - this means the mounted directory is shared between your host and the running container. This statement
As far as I understand Docker simply creates a regular volume elsewhere on my computer and shares that between containers
is true of docker volumes, but not the bind mount type you have used. See e.g., the offical docs or this nice summary post for a nice breakdown of the difference between volume types.