An administrator needs to attach an Elastic Network Interface (ENI) to an application instance in...

ENI Attachment Across Availability Zones:

Elastic Network Interfaces (ENIs) are associated with a specific Availability Zone. They cannot be attached to instances that are in a different Availability Zone than where the ENI was created. Therefore, an ENI created in Availability Zone 1 cannot be attached to an instance in Availability Zone 2 (Option A).

ENI Reattachment:

ENIs can be detached from one instance and reattached to another instance within the same Availability Zone. This flexibility allows for network interface configuration to be preserved across instance changes within the same AZ.

Other Options Analysis:

Option B is incorrect because an ENI can be reattached to any instance in the same AZ.

Option C is incorrect as the primary ENI (eth0) cannot be detached from an instance.

Option D is incorrect because when an ENI is moved, the traffic is directed to the new instance, and there is no redirection to the old instance.

References:

AWS ENI Documentation: Elastic Network Interfaces

AWS Networking Best Practices: AWS Networking