React hot reload doesn't work in docker container

If you are on Windows and use react-scripts 5.x.x or above, CHOKIDAR_USEPOLLING is not working. Make changes your package.json instead in the following way:

    "scripts": {
    ...
    "start": "WATCHPACK_POLLING=true react-scripts start",
    ...
  }

The Dockerfile you have is great for when you want to package your app into a container, ready for deployment. It's not so good for development where you want to have the source outside the container and have the running container react to changes in the source.

What I do is keep the Dockerfile for packaging the app and only build that, when I'm done.

When developing, I can often do that without a dockerfile at all, just by running a container and mapping my source code into it.

For instance, here's a command I use to run a node app

docker run -u=1000:1000 -v $(pwd):/app -w=/app -d -p 3000:3000 --rm --name=nodedev node bash -c "npm install && npm run dev"

As you can see, it just runs a standard node image. Let me go through the different parts of the command:

-u 1000:1000 1000 is my UID and GID on the host. By running the container using the same ids, any files created by the container will be owned by me on the host.

-v $(pwd):/app map the current directory into the /app directory in the container

-w /app set the working directory in the container to /app

-d run detached

-p 3000:3000 map port 3000 in the container to 3000 on the host

--rm remove the container when it exits

-name=nodedev give it a name, so I can kill it without looking up the name

at the end there's a command for the container bash -c "npm install && npm run dev" which starts by installing any dependencies and then runs the dev script in the package.json file. That script starts up node in a mode, where it hot reloads.

Polling wasn't my issue -- watching the docker output I saw it recompiled correctly. My problem was related to networking in the hot loader. I found that the browser is trying to open a websocket back to the node server to ws://localhost:3000/sockjs-node but whatever network settings are like on my computer, this wouldn't route back to the docker container. I added

WDS_SOCKET_HOST=127.0.0.1

to the environment variables. After restarting, the browser successfully connects to ws://127.0.0.1:3000/sockjs-node and hot reloading works properly.

This was tied to using a docker-compose solution similar to the original post. I was able to also make things with with a variation on the docker run approach, but it was much slower to launch.

WSL Workaround for CRA 5.0+

watch.js

const fs = require('fs');
const path = require('path');

if (process.env.NODE_ENV === 'development') {
  const webPackConfigFile = path.resolve('./node_modules/react-scripts/config/webpack.config.js');
  let webPackConfigFileText = fs.readFileSync(webPackConfigFile, 'utf8');

  if (!webPackConfigFileText.includes('watchOptions')) {
    if (webPackConfigFileText.includes('performance: false,')) {
      webPackConfigFileText = webPackConfigFileText.replace(
        'performance: false,',
        "performance: false,\n\t\twatchOptions: { aggregateTimeout: 200, poll: 1000, ignored: '**/node_modules', },"
      );
      fs.writeFileSync(webPackConfigFile, webPackConfigFileText, 'utf8');
    } else {
      throw new Error(`Failed to inject watchOptions`);
    }
  }
}

package.json

"scripts": {
    "start": "node ./watch && react-scripts start",

I had same issue once, This issue was in my Dockerfile The workdir was /var/app/ while in my docker-compose.yml I mounted current working directory to /var/app/frontend, I just removed that /frontend and works fine. please check yours. thanks