If you already followed this post and created a Route 53 record for your sub domain, that means we can proceed to add TXT records now.
So you have few instances attached to a load balancer on Amazon and want to create a Route 53 entry for it to use the Name Server(NS) entries instead of the load balancer long A record which is not accepted by A record in domains DNS managers.
If you are using Amazon aws with ec2 instances, then i assume you already have the pem file to connect to the instances. Normally you will have different instances for your projects.