This repository demonstrates how to bootstrap a React app using create-react-app and add Docker container and using ENV variables. This is the TL;DR version of normal trial and error to get Docker and ENV variables to work nicely in a React app. The goal is allowing you to package and deploy your app to any environment and adhere to 12-factor-app principles.

You need NodeJS installed on your machine at least version 6, and a general understanding of NPM and how to install, configure, and start a Node app. You don't need experience with React to follow this tutorial, however it is preferred.

In order to test the Docker container you need to be able to perform docker commands. Familiarity with building and running images is preferred.

1. Bootstrap your application with create-react-app

npx create-react-app my-docker-react-app

2. Verify application runs

cd my-docker-react-app
npm install
npm start

Your browser will likely launch a window or tab for http://localhost:3000 and you should see a React icon and welcome screen. If everything is running, then CTRL + C to stop the app and proceed. If it is not working, visit create-react-app's website for instructions and troubleshooting tips for your environment.

Bootstrapped React apps (using create-react-app) strip most environment variables with the exception of NODE_ENV and any variables that are prefixed with REACT_APP_<your var>. For this tutorial we will prefix all variables with REACT_APP_ to work with the default install configuration.

1. Add local ENV variables Add a .env.local file with variables REACT_APP_ENVIRONMENT and REACT_APP_TIMEZONE and some values. (SEE: env.local example but name with . prefix and .gitignore will ignore)

2. Add a Config.js file to centralize ENV variables for use in the application. For a larger application you may want to move this to a lib/ folder.

3. Print variable values on default App.js screen to confirm the application is using them.

4. Verify application runs (using npm start as before)

If you tested the app above, and the values you set in your local environment appear, then proceed to package your app in a container.

1. Add Dockerfile as example in this repository

2. Add run script (this is the secret) Adding a separate script for the CMD of your Dockerfile allows you to inject the container's ENV params during docker run .... If you build your React app in the Dockerfile it will not recognize the ENV variables you pass as arguments when you run it.

3. Set script permissions IMPORTANT chmod +x run to allow Docker to execute the script during the CMD. Alternatively you could add another layer to the Dockerfile and a RUN chmod+x run step.

1. Build docker image

docker build -t myimage .

2. Run image and add ENV variables to container

docker run --name myapp -p 8080:5000 \
-e REACT_APP_ENVIRONMENT=docker \
-e REACT_APP_TIMEZONE=America/Pacific \
--rm myimage

3. Test that your app is running on port 8080 in local browser at http://localhost:8080 and you should see the default screen but the values match ENV variable values passed in your run command.

If you made it this far, then you have successfully extended create-react-app to use environment variables and added a Docker image that allows you to configure your application dynamically to run anywhere!