Why is my docker container not picking up environment variables set in docker-compose?

Question

I have a containerised app

|-- project
    |-- app
        |-- main.py
        |-- settings.py
        |-- Dockerfile
        |-- requirements.txt
    |-- .env
    |-- docker-compose-dev.yaml

I have set environment variables in .env. I use the 'environment:' section in docker-compose-dev.yaml to pass them to the app container, I access them in settings.py and then import them into main.py. They do not seem to be being picked up by the app, but docker-compose docker-compose-dev.yaml config shows them being pulled from .env.

.env

REDIS_HOST=redis
REDIS_PORT=6379

docker-compose-dev.yaml

version: "3.2"
services:
app:
    build: ./app
    container_name: app
    environment:
      - REDIS_HOST:$REDIS_HOST
      - REDIS_PORT:$REDIS_PORT

Running docker-compose -f docker-compose-dev.yaml config gives:

services:
  collector:
    build:
      context: /project/app
    container_name: app
    environment:
      REDIS_HOST:redis: null
      REDIS_PORT:6379: null

app/Dockerfile

FROM python:3.8.7-buster

WORKDIR /app
# set environment variables
ENV PYTHONDONTWRITEBYTECODE 1
ENV PYTHONUNBUFFERED 1
ENV USE_DOCKER=true

COPY requirements.txt requirements.txt
RUN pip3 install -r requirements.txt
COPY . .
CMD ["python", "main.py"]

app/settings.py

import os
import dotenv

BASE_DIR = os.path.dirname(
    os.path.dirname(
            os.path.abspath(__file__)
        )
)


dotenv_file = os.path.join(BASE_DIR, ".env")
if os.path.isfile(dotenv_file):
    print(dotenv_file)
    dotenv.load_dotenv(dotenv_file)

#load_dotenv()
REDIS_HOST = os.environ.get('REDIS_HOST', None)
REDIS_PORT = os.getenv('REDIS_PORT', None)
print(REDIS_HOST)
print(REDIS_PORT)

app/main.py

import logging
import settings
import redis

def main():
    logging.info("redis host: %s", settings.REDIS_HOST)
    logging.info("redis port: %s", settings.REDIS_PORT)
    r = redis.Redis(host=settings.REDIS_HOST,
                    port=settings.REDIS_PORT,
                    db=0,
                    )
if __name__ == "__main__":
    main()

If I run this locally, outside of Docker, then main.py does what I expect: print() and logging.info() both show REDIS_HOST = redis, REDIS_PORT = 6379.

If I run this using docker-compose -f docker-compose-dev.yaml up --build then main.py logs REDIS_HOST and REDIS_PORT as None.

If I include print(os.environ) in main.py and then spin it up with docker-compose, it shows the environment variables declared in the Dockerfile (PYTHONBUFFERED, USE_DOCKER), but not those referenced in docker-compose-dev.yaml (REDIS_HOST, REDIS_PORT).

The 'null's after the variables in the config output give me pause for thought, but I cannot find an explanation for them anywhere.

Any suggestions for what I'm overlooking would be welcome. I have a very similar set-up on another project which works smoothly, so I'm stumped about what's causing this.

jabbson · Accepted Answer · 2021-05-23 16:25:24Z

2

The reason is that the compose yaml lacks spaces between the name and the value from the .env file and also take out the dashes:

environment:
  REDIS_HOST: $REDIS_HOST
  REDIS_PORT: $REDIS_PORT

answered May 23, 2021 at 16:25

jabbson

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