Docker compose is using the env which was built by Dockerfile, instead of using env_file located in docker-compose.yml directory because of webpack

Question

First I want to use my application.env variables on my webpack.config.prod.js, so I did this in my webpack file.

I am successfully able to access process.env.BUILD variables.

My application's env has this configuration -

My nodejs web app is running fine locally, no problem at all. I want to build docker image of this application and need to use docker-compose to create the container.

I built my docker image and everything good so far.

now to create container, instead of docker run. I am using separate folder which consists of docker-compose.yml and.env files. Attached the screenshot below

My docker-compose.yml has this code -

version: '3.9'
services:     
  api:
    image: 'api:latest'
    ports:
      - '17000:17000'
    env_file:
      - .env
    volumes:
      - ./logs:/app/logs
    networks:
      - default

My docker-compose.env has this redis details

My application has this logs -

I started my docker container by doing docker-compose up. Containers created and up and running, but the problem is

In the console, after connecting to redis.. process.env.REDIS_HOST contains the value called 'localhost' (which came from the first env where I used to build docker image). Docker compose.env is not getting accessed.

After spending 5+ hours. I found the culprit, It was webpack. On my initial code, I added some env related things in my webpack right? Once I commented those, taken a new build. Everything is working fine.

But my problem is how I can actually use process.ENV in webpack, also docker-compose need to use the.env from its directory.

Updated -

My DockerFile looks like this:

Just, It will copy the dist which contains bundle.js, npm start will do - pm2 run bundle.js.

Answer 1

From what I know webpack picks up the.env at build time, not at runtime. This means that it needs the environment variables when the image is built.

The one you pass in docker-compose.yml is not used because by then your application is already built. Is that correct? In order to user your.env you should build the image with docker-compose and pass the env variables as build arguments to your Dockerfile.

In order to build the image using your docker-compose.yml, you should do something like this:

version: '3.9'
services:     
  api:
    image: 'api:latest'
    build:
      context: .
      args:
      - REDIS_HOST
      - REDIS_PORT
    ports:
      - '17000:17000'
    volumes:
      - ./logs:/app/logs

Note: the context above points to the current folder. You can change it to point to a folder where you Dockerfile (and the rest of the project is) or you can put your docker-compose.yml together with the rest of the project directly and then context stays . .

In your Dockerfile you need to specify these arguments:

FROM node:14 as build

ARG REDIS_HOST
ARG REDIS_PORT

...

With these changes you can build and run with docker-compose:

docker-compose up -d --build