Custom subdomain for an AWS application

Hey, I am using IONOS as a DNS but pointing the nameserver at Netlify. I now want to add a custom subdomain “app.sitename.com” to an app hosted at AWS at a site with a name similar to ec2.ap-southeast-2.compute.amazonaws.com. Updating the CNAME on the DNS Panel just causes the text “Not Found” to render instead of the application. How do I fix this?

Netlify sitename: alli.netlify.com

Objective: Use app.sitename.com as an alias for ec2.ap-southeast-2.compute.amazonaws.com. If nothing works then I am even content with redirecting app.sitename.com to the ec2 app
Problem: Not Found renders to the DOM instead of the site.

While it seems this is not yet supported: Using a subdomain without a custom domain

What can I do before it is supported?

I am thinking to setup an iframe at another custom domain then use the CNAME solution to point to that, but there must be a better way…

hi there, just to clarify - ar eyou wanting to use Netlify DNS to point to a site that isn’t hosted on Netlify? If yes, than that’s not something we can support - we only allow Netlify DNS to be used for sites that are actually hosted with us.