Elastic Network Interface (ENI)
What is an ENI?
- An ENI is a virtual network interface that you can attach to an EC2 instance.
- It’s a logical networking component in a VPC, acting like a virtual NIC (Network Interface Card).
Info
It enables your EC2 instance to communicate within the VPC and with the internet (if allowed).
Key Components of an ENI
- Primary private IPv4 address
- One or more secondary private IPv4 addresses
- Elastic IP address (optional)
- MAC address
- Security groups
- Source/destination check flag
- Attachment to one EC2 instance at a time
Use Cases
High Availability
You can move an ENI (with its IPs and SGs) between instances, great for failover and automation!
ENI Types
| Type | Description |
|---|---|
| Primary ENI | Created by default when an EC2 instance is launched. Not Detachable |
| Secondary ENI | Additional interfaces manually attached to an instance. Only Secondary ENIs are detachable! |
ENI Limits
ENI Limits (varies by instance type):
- t2.micro: 1 ENI
- Larger types: Up to 15 ENIs
ENI CLI Commands
Attach ENI to EC2
aws ec2 attach-network-interface \
--network-interface-id eni-xxxxxxxx \
--instance-id i-xxxxxxxx \
--device-index 1Detach ENI
aws ec2 detach-network-interface \
--attachment-id eni-attach-xxxxxxxx