Install the PM2 tool
it helps to run the react.js app in the background.
npm install pm2 -g
Create a new file with the name app.config.json below the build folder and add the following snippet.

{
apps : [
{
name : "react-app",
script : "npx",
interpreter: "none",
args: "serve -s build -p 3000"
}
]
}
I’m running my React app on a 3000 port you can change your port number
Run the following pm2 command which will start the app on your cloud instance ( i.e we are using AWS EC2).
pm2 start app.config.json
This command will you show the list of the pm2 running processes.
pm2 list
