docker compose environment varibales are undefined in nodejs container

Question

When trying to console log an environment variable defined in docker-compose the node container returns the value as undefined.

docker-compose.yml

version: "3"

services: 

    api: 
        build: ./api
        ports: 
            - "3004:3004"
        volumes:
            - type: bind
              source: ./api
              target: /usr/src/api
        working_dir: /usr/src/api
        environment: 
            REDIS_HOST: "redis://redis:6379"
            TEST: "123"
        depends_on: 
            - redis
        networks:
            - backend

    redis: 
        image: "redis:latest"
        ports: 
            - "6379:6379"
        networks:
            - backend
networks:
    backend:
        driver: bridge

I've tried changing the yaml syntax to - TEST="123" instead of the key value syntax just to make sure. I'm not sure what the issue could be.

The API dockerfile looks like this:

FROM node:12


# create destination directory
RUN mkdir -p /usr/src/api
WORKDIR /usr/src/api

# copy the app, note .dockerignore
COPY . /usr/src/api

# Install packages
RUN npm i yarn --save
RUN yarn 

# COPY . /src
EXPOSE 3005

CMD ["yarn", "dev"]

NodeJS Snippet:

console.log("redis host! + test");
console.log(process.env.REDIS_HOST, process.env.TEST)

Console log output:

api_1    | redis host! + test
api_1    | undefined undefined

Answer 1

You need to additionally reference the environment variables in the Dockerfile using ARG

ARG REDIS_HOST
ARG TEST