Get Private IP of EC2 Instance for Controller-Based Applications

Answer - A.

The application can use the application metadata to get the private IP address.

The below snapshot from the AWS Documentation shows the information that you can get from the Instance metadata.

Option B is invalid because this cannot be used to get the IP address of the instance.

Option C is invalid because this is not an automated approach.

Option D is invalid because we don't know the type of instance the application is running on.

For more information on AWS Instance Metadata, please refer to the below link-

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-metadata.html

To get the private IP of an EC2 instance that is part of an Autoscaling Group, there are multiple ways to achieve this:

Option A: Query the Instance Metadata Each EC2 instance has metadata associated with it that can be queried by making a request to the metadata service at a well-known IP address (169.254.169.254). This service provides information about the instance, including its private IP address. To retrieve the private IP address of an EC2 instance, you can make an HTTP request to the following URL within the instance: http://169.254.169.254/latest/meta-data/local-ipv4 This will return the private IP address of the instance.

Option B: Query the Instance User Data When launching an EC2 instance, you can provide user data in the form of a script or text that is executed when the instance is first launched. This user data can be used to pass configuration information, launch scripts, and more. To retrieve the private IP address of an EC2 instance using user data, you can include a script that fetches the IP address and then passes it to the application. This script can be run as part of the user data, which is executed when the instance is first launched.

Option C: Have an Admin get the IP address from the console This option is not recommended since it requires manual intervention and is prone to errors. In addition, this method will not work well in a dynamic Autoscaling Group environment where instances are frequently launched and terminated.

Option D: Make the application run IFConfig This option is not recommended since it requires the application to have permissions to run system-level commands like IFConfig, which is not recommended from a security perspective.

In summary, the recommended options to retrieve the private IP address of an EC2 instance that is part of an Autoscaling Group are either to query the instance metadata or pass it as user data during instance launch.