Please refer to Amazon's ELB help content for how to set up ELB at Amazon.
- Log into your Cloudflare account.
- From the dropdown menu on the top left, select your domain.
- Select the DNS settings tab.
- Select the record type as CNAME, add the content value of your ELB domain.
With Cloudflare's CNAME Flattening, using a CNAME at the root or apex record is supported in an RFC-compliant manner, so it's fine to use a CNAME at the root to point to an Elastic Load Balancer.