How to get FQDN of an instance without having an associated elastic IP

Question

Hi,  
  
I'm currently working with a client to replace multiple instances of a wordpress site(one for each location) with a new web app I've been working on and I want to know how I can get the FQDN without an elastic IP? I need to get it without one as there will be more instances of the web app than the current limit of 5 Elastic IPs per account and I am unable to use a single IP for remapping as the sites already exist through another DNS provider(they are not ready to be changed yet) so that I can not create a hosted zone for the domain name.  
  
Thanks.

Answer

You can get the FQDN of any IP address using standard tools nslookup or dig.  They are also shown in the AWS Console.  You can also use a free service like xip.io to make up hostnames pointing to any IP address, for example, 203.0.113.55 could be www.mysite.203.0.113.55.xip.io.  No configuration needed, you just create a hostname and as long as your IP appears immediately to the left of "xip.io" this just works.  I assume there are others like it.  
  
It isn't clear why exactly you would need the FQDN of a public IP address for what you are describing... intuition suggests that perhaps you are trying to solve the wrong problem.  Can you clarify this need?  
  
Also, 5 Elastic IP addresses is only the _default_ limit per region.  All you have to do is write a brief explanation of why you need more, and as long as the description includes a reasonable use case, support will increase the limit.  
  
https://docs.aws.amazon.com/general/latest/gr/aws_service_limits.html

How to get FQDN of an instance without having an associated elastic IP

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