Reading an environment variable in react which was set by docker

You should check next moments

I. You env variables have prefix REACT_APP_

II. In docker file you have ARG and ENV commands like

ARG REACT_APP_DEBUG
ENV REACT_APP_DEBUG=$REACT_APP_DEBUG

III. you pass your arg as build arg in docker-compose.yml it looks like

services:
  my-app:
    build:
      args:
        REACT_APP_DEBUG=True

or in docker build it looks like

docker build -t my_app:dev --build-arg REACT_APP_DEBUG=True .

I would like to thank everyone who posted answers and comments.The problem that I was facing was solved using a combination of these answers and some help from other resources.

As suggested by @DavidMaze (in the comments), I started looking into webpack config present in my code. I found out that the webpack was reading all the environment variables declared inside the container.

So I started experimenting with my Dockerfile and docker-compose.yml as I realized that REACT_APP_HOST_IP_ADDRESS was not being passed as an environment variable when the react was building the code.

The first thing I changed was the Dockerfile. I statically declared the IP inside dockerfile for testing
ENV REACT_APP_HOST_IP_ADDRESS localhost. By doing this I was able to see the value localhost inside the env variables which were read by webpack.

Now I tried passing the ENV Variable from docker-compose to dockerfile as suggested by @Alex in his answer, but it didn't work.

So I referred to https://github.com/docker/compose/issues/5600 and changed the docker-compose.yml and Dockerfile as follows

docker-compose.yml

version: '2'
services:
  nginx:
    container_name: ui
    build:
      context: nginx/
      args:
        REACT_APP_HOST_IP_ADDRESS: ${IP_ADDRESS}
    ports:
      - "80:80"

where IP_ADDRESS is exported as an env variable.

Dockerfile

FROM node:8 as ui-builder

WORKDIR /home/ui

COPY helloworld .

RUN npm install

ARG REACT_APP_HOST_IP_ADDRESS

ENV REACT_APP_HOST_IP_ADDRESS $REACT_APP_HOST_IP_ADDRESS

RUN npm run build

FROM nginx
COPY --from=ui-builder /home/ui/build /usr/share/nginx/html
CMD ["nginx", "-g", "daemon off;"]

React Component

import React, { Component } from 'react';

class HelloWorld extends Component {
  render() {
    console.log(process.env.REACT_APP_HOST_IP_ADDRESS);
    return (
      <div className="helloContainer">
        <h1>Hello, world!</h1>
      </div>
    );
  }
}

export default HelloWorld;

This configuration makes available the variables passed via ARG in docker-compose to Dockerfile during the image build process and hence the variables can be in turn declared as env variables which React can use during build process provided the webpack reads the env variables.

The webpack will be able to read the env variables using DefinePlugin https://webpack.js.org/plugins/define-plugin/.

Make sure you prefix your variables with REACT_APP_ (as seen here), otherwise it won't be picked up by React.

Env variables should start with REACT_APP_ otherwise NODE_ENV variables are a bit confused and your environment variable will not work:

environment:
  - REACT_APP_DEBUG=TRUE

Otherwise, docker-compose.yml is not valid and you will see an error message:

services.client.environment contains an invalid type, it should be an object, or an array

Here is a working sample:

docker-compose.yml

version: "3.3"

services:
  client:
    container_name: client
    environment:
      - REACT_APP_DEBUG=TRUE
    build:
      dockerfile: Dockerfile
      context: ./web/client

Dockerfile

FROM node:6.0.0

# Set env variable
ARG REACT_APP_DEBUG
ENV REACT_APP_DEBUG=$REACT_APP_DEBUG

# that will be empty
RUN echo "DEBUG": $REACT_APP_DEBUG

Run:

->docker-compose run  client node
->process.env.REACT_APP_DEBUG 
'TRUE'

I checked how it's done in API Platform, config just defines consts based on env ('.env' file):

export const API_HOST = process.env.REACT_APP_API_ENTRYPOINT;
export const API_PATH = '/';

Importing this you have one value (API_HOST) while process.env.HOST_IP_ADDRESS refers to deep object structure unavailable at runtime.