How to access environment variables in react from docker and webpack

Question

I have a react front-end application that is being built via webpack and containerised using docker.

Goal: Is to be able to define environment variables in docker and be able to access the environment variables in my reactjs application.

docker-compose.yml

version: '3'

services:
  portal:
    build:
      context: .
      dockerfile: Dockerfile
    environment:
      - NODE_ENV=production
      - PORT=8080
      - API_URL=http://test.com
    ports:
      - "8080:8080"

For example i want to access this api_url variable in my reactjs app

webpack.prod.js

const path = require('path');
const nodeExternals = require('webpack-node-externals');
const WebpackShellPlugin = require('webpack-shell-plugin');
const CopyWebpackPlugin = require("copy-webpack-plugin");
const {CleanWebpackPlugin} = require('clean-webpack-plugin');
const webpack = require('webpack');
const dotenv = require('dotenv');

console.log(process.env);

module.exports = [{
    entry: {
        app1: ["./src/public/app1/index.tsx"],

    },
    mode: NODE_ENV,
    watch: NODE_ENV === 'development',
    output: {

        filename: "[name]/bundle.js",
        path: path.resolve(__dirname, 'build/public/'),
    },

    // Enable sourcemaps for debugging webpack's output.
    devtool: "source-map",

    resolve: {
        // Add '.ts' and '.tsx' as resolvable extensions.
        extensions: [".ts", ".tsx", ".js", ".json", ".css", ".scss"]
    },

    module: {
        rules: [
            { test: /\.tsx?$/, loader: "awesome-typescript-loader" },


            // All output '.js' files will have any sourcemaps re-processed by 'source-map-loader'.
            { enforce: "pre", test: /\.js$/, loader: "source-map-loader" },

            { test: /\.scss$/, use: [ 
                { loader: "style-loader" },  // to inject the result into the DOM as a style block
                { loader: "css-loader", options: { modules: true } },  // to convert the resulting CSS to Javascript to be bundled (modules:true to rename CSS classes in output to cryptic identifiers, except if wrapped in a :global(...) pseudo class)
                { loader: "sass-loader" },  // to convert SASS to CSS
            ] }, 
        ]
    },
    "plugins": [
        // new CleanWebpackPlugin(),
        new webpack.DefinePlugin({
            'process.env.API_URL': JSON.stringify(process.env.API_URL)
        }),

        new CopyWebpackPlugin([
            {
                from: "src/public/app1/index.html",
                to: "app1"
            },
        ]),
    ],



    // When importing a module whose path matches one of the following, just
    // assume a corresponding global variable exists and use that instead.
    // This is important because it allows us to avoid bundling all of our
    // dependencies, which allows browsers to cache those libraries between builds.
    externals: {
        // "react": "React",
        // "react-dom": "ReactDOM"
    }
}]

You can see im trying to set the environment variables in webpack with the following plugin

   new webpack.DefinePlugin({
                'process.env.API_URL': JSON.stringify(process.env.API_URL)
            }),

Problem: You can see i have console logged process.env in my webpack config BUT none of the environment variables i set in the docker are shown.

Context:

DockerFile

FROM node:10.16.0-alpine
# Bundle APP files
WORKDIR /app
COPY ./ /app/
# Install app dependencies
ENV NPM_CONFIG_LOGLEVEL warn
RUN npm ci
RUN npm run build

npm

"build": "webpack --config webpack.prod.js",

Answer 1

The environment variables in your docker-compose.yml file will only be made available when your container starts.

If you want them available during the build as well, then you can use build args:

version: '3'

services:
  portal:
    build:
      context: .
      dockerfile: Dockerfile
      args:
        - NODE_ENV=production
        - PORT=8080
        - API_URL=http://test.com
    ports:
      - "8080:8080"

Then, in your Dockerfile, declare the build args using the ARG command, and then declare the ENV variables, setting them to the value of the build args:

FROM node:10.16.0-alpine

# Build args
ARG NODE_ENV
ARG PORT
ARG API_URL

# Environment vars
ENV NODE_ENV=$NODE_ENV
ENV PORT=$PORT
ENV API_URL=$API_URL

# Bundle APP files
WORKDIR /app
COPY ./ /app/

# Install app dependencies
ENV NPM_CONFIG_LOGLEVEL warn
RUN npm ci
RUN npm run build

I hope this helps.