Search the web for a starter project for that configuration I found only out-of-date solutions, so I've built my own.
How to run React on App Engine?
I've decide to use create-react-app and I've create the required npm scripts to run it locally and deploy it to App Engine.
Use this command to run both Webpack dev-server and App Engine dev-server for development. Both of the dev-servers support hot-reload so you can use your favorite text editor to edit both React and App Engine code, save it and you have the latest code already in the browser without refresh anything.
npm run deploy
Use this command to deploy the app to App Engine. I'm reading configuration from package.json under "appEngine" to decide which app to push to.
For all the other details page see the github readme.