Route 53 name server collisions

Question

Let's say I create a Hosted Zone in Route 53 for mydomain.com after purchasing that domain name through the Route 53 registrar service within my account, which we will call Account 1.  
  
AWS will assign a set of four authoritative name servers for mydomain.com. Let's say that one of them is ns-1234.awsdns-56.net.  
  
Now let's say that someone else, within an account we will call Account 2, an account that does not own mydomain.com, creates a Hosted Zone in Route 53 for mydomain.com (even though they do not own that domain name).  
  
AWS will assign a set of four name servers in Account 2 for mydomain.com. Let's say that by coincidence one of them happens to be ns-1234.awsdns-56.net.  
  
Is this scenario possible? Does AWS re-use the name servers assigned to hosted zones?  
  
If this scenario is possible, what would happen if a DNS query arrived at ns-1234.awsdns-56.net for www.mydomain.com, if additionally Account 1 (the one that owns mydomain.com) had created an A record for www.mydomain.com pointing to 1.1.1.1, and Account 2 (which uses the same name server but does not own mydomain.com) had created an A record for www.mydomain.com pointing to 2.2.2.2?

Answer

Hi,  
  
Every time anyone creates a hosted zone for a given domain name, such as example.com, Route 53 assigns a unique set of four name servers to that hosted zone. This is true regardless of which account creates yet another example.com hosted zone, so there will never be a conflict.   
  
On a side note, there are only so many unique combinations of Route 53 name servers, which explains why you can no longer create a hosted zone named example.com--the maximum possible number of unique combinations of name servers for example.com hosted zones have already been assigned.  
  
Scott

Route 53 name server collisions

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