docker-compose django unable to connect to postgres - django

Question

I'm trying to dockerize an existing django application. I've followed the example docker-compose and docker files on https://docs.docker.com/samples/django/
I've added the links and networks suggestion as see on other posts, to no avail.
I've brought up the db by itself with docker-compose up db and run docker ps and confirmed it's up, accepting connections, and has the name db. I'm not sure what else to try.
My docker-compose:
version: '3'
services:
db:
image: postgres
volumes:
- ./data/db:/var/lib/postgresql/data
environment:
- POSTGRES_DB=postgres
- POSTGRES_USER=postgres
- POSTGRES_PASSWORD=postgres
container_name: db
networks:
harpnetwork:
harp:
build:
context: .
dockerfile: docker/harp/Dockerfile
volumes:
- ./harp:/harp
environment:
- POSTGRES_DB=postgres
- POSTGRES_USER=postgres
- POSTGRES_PASSWORD=postgres
ports:
- 16765:16765
depends_on:
- db
networks:
harpnetwork:
links:
- db:db
networks:
harpnetwork:
My django db config:
DATABASES = {
'default': {
'ENGINE': 'django.db.backends.postgresql',
'NAME': os.environ.get('POSTGRES_NAME'),
'USER': os.environ.get('POSTGRES_USER'),
'PASSWORD': os.environ.get('POSTGRES_PASSWORD'),
'HOST': 'db',
'PORT': 5432,
}
}
and my Dockerfile to build the django project
From python:3.10
COPY ./harp harp
WORKDIR /harp
RUN pip install -r requirements.txt
RUN python manage.py migrate
CMD ["python", "manage.py", "runserver", "0.0.0.0:16765"]