I'm trying to write a small docker(-compose) deployment solution for a small Django application.
Currently, the django-compose file, named docker-compose.dev.yaml looks something like this:
version: "3"
services:
backend:
build:
context: ./backend
dockerfile: Dockerfile
command: python manage.py runserver 0.0.0.0:8000
ports:
- 8000:8000
env_file:
- dev.env
The file dev.env looks like this:
DEBUG=1
SECRET_KEY=We9ZyuSKsP9Mgvsrt74gExF8baWbGL # not important that this leaks
DJANGO_ALLOWED_HOSTS=localhost
However, when django tries to start, I get the following:
#11 0.634 ALLOWED_HOSTS = os.environ.get("DJANGO_ALLOWED_HOSTS").split(" ")
#11 0.634 AttributeError: 'NoneType' object has no attribute 'split'
Basically, the environment variable is returning None, meaning the variables aren't getting onto the container.
I tried, according to the docs, to do this:
# ...
environment:
- DEBUG
- SECRET_KEY
- DJANGO_ALLOWED_HOSTS
Without any luck.
Any ideas? The repository behind the code is public, I invite you to try.
My current test environment is Docker desktop on Windows 10.
So, I figured it out.
Turns out that this line in the Dockerfile for the backend:
RUN python manage.py migrate
Was the problem. I didn't realize it ran at build time, not at runtime, so the environment variables weren't available.
I moved into a script called at runtime and not it all works!
backend/Dockerfile:
# ...
# Make files executable
RUN chmod +x start.dev.sh
backend/start.dev.sh:
#!/bin/bash
python manage.py migrate
python manage.py runserver 0.0.0.0:8000
And ./docker-compose.dev.yaml:
# ...
command: ./start.dev.sh
# ...