Deploying a static website on S3 but using domain name from 123Reg

Whilst you could add a CNAME record to point to your S3 Website URL, this can cause issues specifically when using HTTPS (e.g. CORS).

If your registrar offer that option, you can delegate the DNS handling for your Domain to Route53. You can find more information on this process in the Developer Guide for Route53.

There is also a Video available which guide you through this process.