Best Practices for Configuring Network InterfacesYou can attach a network interface to an instance when it's running (hot attach), when it's stopped(warm attach), or when the instance is being launched (cold attach). You can detach secondary (ethN) network interfaces when the instance is running or stopped. However, you can't detach theprimary (eth0) interface.You can attach a network interface in one subnet to an instance in another subnet in the same VPC,however, both the network interface and the instance must reside in the same Availability Zone.When launching an instance from the CLI or API, you can specify the network interfaces to attach tothe instance for both the primary (eth0) and additional network interfaces. Launching an instancewith multiple network interfaces automatically configures interfaces, private IP addresses, and routetables on the operating system of the instance. A warm or hot attach of an additional networkinterface may require you to manually bring up the second interface, configure the private IPaddress, and modify the route table accordingly. (Instances running Amazon Linux automaticallyrecognize the warm or hot attach and configure themselves.) Attaching another network interface toan instance is not a method to increase or double the network bandwidth to or from the dual-homedinstance. Reference: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-eni.html#use-network-and-securityappliances-in-your-vpc