What prevents Route 53 public and private same hosting addresses from colliding?

Route53 prioritizes private hosted zone over public hosted zone if the domain name is exactly "same". For ex) VPC A has private hosted zone associated with it for "abc.com" and there is actually a public hosted zone "abc.com". Any record lookup under abc.com from the VPC will go to private hosted zone and if the record is not present you would get a NXDomain (it will not search the public hosted zone)

When you see that there are two sub-domains, one being resolved internally and one publicly the scenario would be as follows:

• VPC A has private hosted zone for "internal.abc.com" and there is a public hosted zone for "abc.com". --> If you lookup for anything under internal.abc.com, for ex, "talk.internal.abc.com" the answer is from the private hosted zone. (If record is not present it will not fall back to public hosted zone) --> If you lookup for anything else under "abc.com" for ex, "dd.abc.com" , the request would be sent to the public hosted zone.

In this scenario, there is no exact match so we choose the longest match for resolution and hence longest match for "talk.internal.abc.com" is "internal.abc.com" (Private hosted zone) and not "abc.com" (public hosted zone). However for ""dd.abc.com" the longest prefix match will be "abc.com"(public hosted zone).