Adding a CNAME record to Client's DNS

After Network Load Balancer is provisioned, it will have a domain name, for example

caddy-Publi-JRJUD8MD0RLE-671e55804baa69eb.elb.us-west-2.amazonaws.com

You only need to give this domain name to your client, and he/she will create a CNAME record in their DNS. For example:

And your client's domain (c21.awscustomdomainmanager.xyz) will have access to your service.