Warning

Stopping and restarting the instance after adding a second network interface will release any automatically assigned public IP address. If several interfaces are required where one or more are configured with a public address, use Elastic IP addresses.
Additionally, adding a second IP network interface with an IP configuration to a non-Amazon Linux EC2 instance causes traffic flow issues. This occurs in cases of asymmetric routing where traffic to the instance arrives at one network interface and leaves the instance through the other network interface. This is blocked by AWS because of a mismatch between MAC address and IP address. Refer to the AWS documentation and the Charon-SSP Cloud Networking chapter (section asymmetric routing considerations) for more information. Failure to use the proper steps, may make your instance unreachable!
If your instance supports enhanced networking there may be naming inconsistencies when adding additional interfaces to a running instance. Please refer to the interface naming section below and the AWS documentation.
The NetworkManager is disabled on Charon-SSP AWS marketplace images. Therefore, ifcfg-files in /etc/sysconfig/network-scripts are required to define the IP configuration of an interface.

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Interface Naming on Linux Hosts with Enhanced Networking

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On instances without support for enhanced networking the Linux interface names are also usually eth0, eth1, etc.
However, on instances with support for enhanced networking, the names on the AWS level differ from those on the Linux level there may be a naming inconsistency after adding a second interface to the instance:
The first (primary) interface is called ensX (where X is an integer denoting the interface number; example: ens5).
When a second interface is added to a running instance, it may initially be called eth0.
However, the command `ethtool -i eth0` shows that the enhanced network driver (ena) will be used for this interface. This interface will change its name to ensY (where Y is X+1) after restarting the instance. This means that any configuration file created for this interface must use the final name of the interface instead of eth0. Otherwise, the instance may become unreachable after a restart because there is no valid interface configuration (NetworkManager is not enabled on Charon-SSP AWS, so a configuration file must exist to configure the interface properly).
Please note: this numbering sequence may change in the future. It is based on the PCI slot on which the Ethernet controller is presented and which is incremented by one for each additional Ethernet interface added. On the Charon host system, the slot can be verified with the following command:
`# lspci -vv | grep -A20 Ethernet`
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