How To Route 53 Record to AWS Public IP: Expected Behavior Explained

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If you’re working with AWS, it’s important to understand how public IP addresses and DNS records behave, especially to prevent potential security issues like subdomain takeovers. Here’s a simple guide to help you manage this effectively.

When you stop or terminate an EC2 instance that has a public IPv4 address assigned automatically, AWS releases that IP back into its pool of available addresses. This means the same IP could be reassigned to another customer later. The only time your IP remains tied to your account is if you use an Elastic IP, which stays allocated to you until you choose to release it.

AWS does not verify whether DNS records in Route 53 still point to active resources. Since Route 53 is just a DNS service, it will return any record that exists, whether or not the backend resource is still live. This can create a risk when IP addresses are reused because your DNS record might point to an IP now owned by someone else.

This situation can lead to a subdomain takeover, where traffic intended for your subdomain might reach someone else’s resource, especially if the IP address has been reassigned. It’s a common risk in cloud environments due to the ephemeral nature of public IPs.

To protect your infrastructure, it’s best to follow these recommended practices:
– Use Elastic IPs whenever possible for public IP addresses.
– Set up Route 53 Alias records pointing to resources like Application Load Balancers, Network Load Balancers, CloudFront distributions, or API Gateways instead of using raw IP addresses.
– Automate DNS management with Infrastructure as Code tools such as CloudFormation or Terraform, so records are updated or removed when resources are deleted.
– Regularly review your DNS records to ensure none are pointing to orphaned or ephemeral IPs.
– Avoid leaving long-term DNS entries that point directly to temporary infrastructure.

In summary, keep in mind that AWS may reuse public IPv4 addresses, and Route 53 doesn’t validate whether associated resources still exist. Being proactive with DNS management and adopting architecture best practices can prevent unintended exposure or security risks. Staying disciplined in your operational procedures is key to maintaining a secure environment.