AWS Getting Started - Create and Add a Secondary NIC

If during instance creation you are not able to add a secondary Network Interface (necessary for high availability). the second network interface can be added after instance creation. 

• From the EC2 dashboard, scroll down the left panel to Network & Security.
• Select Network Interface.
• Click Create Network Interface.

Next, create the network interface. 

1. Description - Provide a description to describe your network interface.
2. Subnet - Select the desired subnet to match the instance it will be assigned to.
3. Private IPv4 address - Select auto-assign.
4. Security groups - Select the security group assigned to your instance.
5. Tags - Create any tags that you want to be assigned to your network interface.
6. Once configuration is complete, click Create network interface.

• Select the network interface created. Click Actions > Attach. 

• Select the instance you wish to attach the additional NIC. Click Attach.

• To verify the network interface has been added, select your instance from Instances in the EC2 dashboard.
• Scroll down the Networking tab and look for Network Interfaces.