django-celery netcat spam within docker container - django

Question

I am trying to run celery in a separate docker container alongside a django/redis docker setup.
When I run docker-compose up -d --build, my logs via docker-compose logs --tail=0 --follow show the celery_1 container spamming the console repeatedly with
Usage: nc [OPTIONS] HOST PORT - connect
nc [OPTIONS] -l -p PORT [HOST] [PORT] - listen
-e PROG Run PROG after connect (must be last)
-l Listen mode, for inbound connects
-lk With -e, provides persistent server
-p PORT Local port
-s ADDR Local address
-w SEC Timeout for connects and final net reads
-i SEC Delay interval for lines sent
-n Don't do DNS resolution
-u UDP mode
-v Verbose
-o FILE Hex dump traffic
-z Zero-I/O mode (scanning)
I am able to get celery working correctly by removing the celery service from docker-compose.yaml and manually running docker exec -it backend_1 celery -A proj -l info after docker-compose up -d --build. How do I replicate the functionality of this manual process within docker-compose.yaml?
My docker-compose.yaml looks like
version: '3.7'
services:
backend:
build: ./backend
command: python manage.py runserver 0.0.0.0:8000
volumes:
- ./backend/app/:/usr/src/app/
ports:
- 8000:8000
env_file:
- ./.env.dev
depends_on:
- db
- redis
links:
- db:db
celery:
build: ./backend
command: celery -A proj worker -l info
volumes:
- ./backend/app/:/usr/src/app/
depends_on:
- db
- redis
redis:
image: redis:5.0.6-alpine
command: redis-server
expose:
- "6379"
db:
image: postgres:12.0-alpine
ports:
- 5432:5432
volumes:
- /tmp/postgres_data:/var/lib/postgresql/data/

Answer 1

I found out the problem was that my celery service could not resolve the SQL host. This was because my SQL host is defined in .env.dev which the celery service did not have access to. I added
env_file:
- ./.env.dev
to the celery service and everything worked as expected.