How can an EC2 instance find both its private and public IP addresses?

An EC2 instance can access its private and public IP addresses by retrieving instance metadata from the special IP address 169.254.169.254. This address is part of the link-local IP address range that is reserved for instances to access metadata, which includes a wealth of information about themselves, such as their instance ID, AMI ID, and various types of network information.

When an instance queries the metadata service at the specified URL, it can request information about its network interfaces, which includes both the private and public IP addresses. The response is a structured JSON object that provides the details necessary for the instance to understand its network configuration.

This method is particularly useful because it enables the instance to retrieve its network information dynamically and programmatically, allowing applications or scripts running on the instance to adjust their behavior based on the addresses assigned.

Other methods, such as checking the EC2 console or using the AWS CLI, are not direct methods for the instance to obtain this information. The console provides a visual interface for users but isn't accessible from the instance itself. The AWS CLI would require appropriate permissions and setup to work from an instance context, whereas reading a log file generated at boot may not always include IP address information depending on logging configuration and what data is collected