An Elastic Network Interface is a virtual network card you can attach to an EC2 instance. It carries a private IP, security groups, and MAC address — and can be moved to another instance for failover.
Why it matters
An ENI can be detached from a failed instance and attached to a standby, preserving its IP and settings — useful for management networks and failover. Instances can also have multiple ENIs (e.g., one for management, one for production traffic). The tell is “move a fixed network identity between instances” or “multiple network interfaces.”
Test yourself
An administrator wants a fixed private IP and its security groups to move quickly from a failed EC2 instance to a standby. What enables this?
- An Elastic IP only
- Detaching and attaching an Elastic Network Interface
- A new subnet
- A larger instance type
👉 Click to reveal the answer & explanation
Correct answer: B. An ENI carries a private IP, MAC, and security groups and can be moved between instances, preserving the network identity for failover. An Elastic IP (A) is a public address only; a new subnet (C) or bigger instance (D) doesn’t move the interface’s settings.
Related topics
Amazon EC2 · Elastic IP · Amazon VPC
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