How can software determine the public and private IP addresses of the Amazon EC2 instance that it is running on?
Query the local instance metadata.
Query the appropriate Amazon CloudWatch metric.
Query the local instance userdata.
Use ipconfig or ifconfig command.
Explanations:
The local instance metadata provides a reliable API for EC2 instances to retrieve information about themselves, including both public and private IP addresses. This metadata is accessible at a special IP address (169.254.169.254) and contains various details specific to the instance, such as network configuration.
Amazon CloudWatch metrics are primarily used for monitoring AWS resources and do not provide direct information about an instance’s public or private IP addresses. CloudWatch metrics focus on performance and operational data rather than instance-specific network details.
Instance userdata is primarily used for configuration purposes when the instance launches and does not provide current instance network information like IP addresses. Userdata scripts are executed on instance startup and are not a reliable source for querying IP addresses post-launch.
Theipconfigcommand (on Windows) orifconfigcommand (on Linux) can provide local network configuration details, but they do not reliably indicate the public IP address of the instance. The public IP is typically not exposed directly through these commands, as it is managed by AWS infrastructure and requires access to instance metadata to obtain.