Hey anurag, big fan of Render!
We currently don't have a great solution for this and we recommend that users use a DNS provider that has support for something like an ALIAS record.
Good question! One of the motivations for splitting our infrastructure into clusters was to separate paying and non-paying customer. There's various reason for this, reducing the size of our failure domains and running better hardware for paying customers. However, this means users can be transitioned between clusters as they become a paying customer or back to a non-paying customer. Since repl.co subdomains are tied to the user/repl and not to the particular back-end cluster, we'd have to maintain way too many records with our existing DNS provider. Even if we could, we'd need to make sure the records are always synchronized. In the end, it made more since to roll our own authority server that can just query our data store and generate the right DNS answers on the fly.
