How to deploy separated frontend and backend?

node.js reactjs deployment frontend backend

I just answered a related question for AWS.

You can deploy

your frontend on a static hosting service and a CDN
- AWS S3 + AWS CloudFront
- Google Cloud Storage + Google Cloud CDN
- GitHub Pages + CloudFlare
- Now
- Surge
- Netlify
- etc
your backend on a cloud computing service
- AWS Elastic beanstalk or AWS EC2
- Google App Engine
- Now
- Heroku
- etc

You can set different subdomains on different hosts, e.g.

app.domain.com on GitHub Pages
api.domain.com on Heroku