Reading an environment variable in react which was set by docker

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'

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 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.

Here is my solution using ENV in my Dockerfile, DefinePlugin in the webpack.config.js and process.env in my javascript codes:

First set you environment variable and its value in your Dockerfile :

...
RUN npm install
ENV MY_ENV_VAR my_env_value
...

Then using DefinePlugin plugin, add it to process.env in webpack.config.js:

const webpack = require('webpack');
...
  plugins: [
    new webpack.DefinePlugin({
      'process.env.MY_ENV_VAR': JSON.stringify(env.MY_ENV_VAR),
    }),
  ],
...

And finally use the env variable in your code:

const host = process.env.MY_ENV_VAR || 'a_default_value_in_case_no_env_is_found';

I use Github CI to set secrets per env. First in GH action file I use run: docker build ... --build-arg REACT_APP_APIURL=${{ secrets.REACT_APP_APIURL }} .

Then I use them in Dockerfile in my repo to build there final image with the React app like:

ARG REACT_APP_APIURL
RUN test -n "$REACT_APP_APIURL" || (echo "REACT_APP_APIURL not set in GH/your environment" && false)
...
RUN npm run build

This value is used in the npm run build automatically (used in my react typescript codebase as process.env.REACT_APP_APIURL). I chose to check for this value and let the app fail immediately on load if something is wrong with my Docker image or configuration somewhere.

export const config = {
  apiUrl: setApiUrlFromEnv(),
};
  
function setApiUrlFromEnv() {
  if (process.env.REACT_APP_APIURL) {
    return process.env.REACT_APP_APIURL;
  } else {
    // if something goes wrong in setup, do not start app and show err directly in web console
    throw new Error(
      `ENV not configured properly (REACT_APP_APIURL) to use desired ENV variables (${process.env.REACT_APP_APIURL})`
    );
  }
}

Step 1: Add args for env to docker-compose file

We use args instead of environment field because environment fields are not available on build stage

services:
    ...
    web_app:
        build:
          context: .
          dockerfile: Dockerfile
          args:
            - MY_ENV=HELLO_WORLD

Step 1_alternative: If image is built by cloudbuild instead of docker-compose, we should add args to cloudbuild.yml file

steps:
- name: ...
    args:
    ...
    - --build-arg
  - MY_ENV=HELLO_WORLD

Step: 2: Add ARGS and ENVS to dockerfile

We use ARG command to get variables from docker-compose args

We use ENV to set env for the build

ARG MY_ENV

ENV MY_ENV=$MY_ENV

RUN echo "$MY_ENV"

Step 3: Update webpack config

• Use webpack.ProvidePlugin({ process: "process/browser" }) to enable process in web app
• Use webpack.DefinePlugin to define env variables available in web app
• Add process library to dev dependency by npm i -S process

plugins: [
    new webpack.ProvidePlugin({
      process: "process/browser"
    }),
    new webpack.DefinePlugin({ "process.env": JSON.stringify(process.env) })
  ]