An Elastic Network Interface (ENI) is a virtual network interface that you can attach to an EC2 instance in a Virtual Private Cloud (VPC), representing a logical networking component that includes a primary private IPv4 address, one or more secondary IPv4 addresses, an Elastic IP address, a MAC address, and security groups.

An Elastic Network Interface (ENI) is a virtual network interface that you can attach to an EC2 instance in a Virtual Private Cloud (VPC). It is a logical networking component that includes a primary private IPv4 address, one or more secondary private IPv4 addresses, an Elastic IP address, a MAC address, and security groups. ENIs are fundamental to how EC2 instances communicate within a VPC, with the internet, and with other AWS services. Each EC2 instance has a default ENI (the primary network interface) attached at launch, but you can create and attach additional ENIs to create multi-homed networks or specialized network appliances.

ENI Properties

Use Cases for Additional ENIs

1
Management Network: Create a separate management network interface for administrative traffic, isolating it from application traffic
2
Network Appliances: Use multiple ENIs in a dual-homed configuration for appliances like firewalls or load balancers
3
High Availability: Quickly move a failed application's ENI to a standby instance for fast failover
4
Logging and Monitoring: Dedicate an ENI for log collection or monitoring traffic without affecting primary network performance
5
Multi-Subnet Deployment: Attach an instance to multiple subnets, useful for scenarios requiring access to resources in different subnets