Where I work, we have many subdomains of our main domain pointing to ELB instances (with CNAME records) that are no longer in use (like my-loadbalancer-1234567890.us-west-2.elb.amazonaws.com). I realize this is a bad practice, but our developers seem to have done this a lot.

How dangerous is it that we have these DNS records? Can someone claim these instance names and start serving content on our subdomains?

As far as I know, every ELB instance's name contains 10 random digits that aren't controlled by the user. Is this correct? Can a user influence the generation of these digits in any way?


No one can intentionally claim those names since they are assigned randomly, as you noted. I'd recommend regardless that you consider using Cloudformation, Terraform, or another tool to manage creation and cleanup of environments. While the situation you describe probably isn't particularly risky; if DNS records aren't being maintained you have to ask what else isn't.

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