Cannot GET / error running hello world in webpack

Turns out I had index.html in the wrong place. From the webpack docs:

To load your bundled files, you will need to create an index.html file in the build folder from which static files are served (--content-base option).

I made a copy of index.html in a new folder I called deployment to match what I specified in the output.path

In webpack-dev-server documentation, there is an writeToDisk option to solve this problem docs. It will store all files on disk instead of memory. Example from my config:

devServer: {
    port: 3000,
    writeToDisk: true,
    proxy: {
        '/': 'http://localhost:8080'
    }
}

In the webpack.config.js put this :

devServer: {
  historyApiFallback: true,
}